diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/activities/MainActivity.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/activities/MainActivity.kt
index 033d3b0a..c55a404a 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/activities/MainActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/activities/MainActivity.kt
@@ -13,6 +13,7 @@ import com.simplemobiletools.calculator.databases.CalculatorDatabase
 import com.simplemobiletools.calculator.dialogs.HistoryDialog
 import com.simplemobiletools.calculator.extensions.config
 import com.simplemobiletools.calculator.extensions.updateViewColors
+import com.simplemobiletools.calculator.extensions.updateWidgets
 import com.simplemobiletools.calculator.helpers.*
 import com.simplemobiletools.commons.extensions.*
 import com.simplemobiletools.commons.helpers.LICENSE_AUTOFITTEXTVIEW
@@ -24,8 +25,11 @@ import me.grantland.widget.AutofitHelper
 class MainActivity : SimpleActivity(), Calculator {
     private var storedTextColor = 0
     private var vibrateOnButtonPress = true
+    private var storedUseCommaAsDecimalMark = false
+    private var decimalSeparator = DOT
+    private var groupingSeparator = COMMA
 
-    lateinit var calc: CalculatorImpl
+    private lateinit var calc: CalculatorImpl
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
@@ -34,26 +38,28 @@ class MainActivity : SimpleActivity(), Calculator {
 
         calc = CalculatorImpl(this, applicationContext)
 
-        btn_plus.setOnClickListener { calc.handleOperation(PLUS); checkHaptic(it) }
-        btn_minus.setOnClickListener { calc.handleOperation(MINUS); checkHaptic(it) }
-        btn_multiply.setOnClickListener { calc.handleOperation(MULTIPLY); checkHaptic(it) }
-        btn_divide.setOnClickListener { calc.handleOperation(DIVIDE); checkHaptic(it) }
-        btn_percent.setOnClickListener { calc.handleOperation(PERCENT); checkHaptic(it) }
-        btn_power.setOnClickListener { calc.handleOperation(POWER); checkHaptic(it) }
-        btn_root.setOnClickListener { calc.handleOperation(ROOT); checkHaptic(it) }
+        btn_plus.setOnClickOperation(PLUS)
+        btn_minus.setOnClickOperation(MINUS)
+        btn_multiply.setOnClickOperation(MULTIPLY)
+        btn_divide.setOnClickOperation(DIVIDE)
+        btn_percent.setOnClickOperation(PERCENT)
+        btn_power.setOnClickOperation(POWER)
+        btn_root.setOnClickOperation(ROOT)
+        btn_minus.setOnLongClickListener { calc.turnToNegative() }
 
-        btn_minus.setOnLongClickListener {
-            calc.turnToNegative()
+        btn_clear.setVibratingOnClickListener { calc.handleClear() }
+        btn_clear.setOnLongClickListener {
+            calc.handleReset()
+            true
         }
 
-        btn_clear.setOnClickListener { calc.handleClear(); checkHaptic(it) }
-        btn_clear.setOnLongClickListener { calc.handleReset(); true }
-
         getButtonIds().forEach {
-            it.setOnClickListener { calc.numpadClicked(it.id); checkHaptic(it) }
+            it.setVibratingOnClickListener { view ->
+                calc.numpadClicked(view.id)
+            }
         }
 
-        btn_equals.setOnClickListener { calc.handleEquals(); checkHaptic(it) }
+        btn_equals.setVibratingOnClickListener { calc.handleEquals() }
         formula.setOnLongClickListener { copyToClipboard(false) }
         result.setOnLongClickListener { copyToClipboard(true) }
 
@@ -61,6 +67,7 @@ class MainActivity : SimpleActivity(), Calculator {
         AutofitHelper.create(formula)
         storeStateVariables()
         updateViewColors(calculator_holder, getProperTextColor())
+        setupDecimalSeparator()
         checkWhatsNewDialog()
         checkAppOnSDCard()
     }
@@ -75,6 +82,11 @@ class MainActivity : SimpleActivity(), Calculator {
             window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
         }
 
+        if (storedUseCommaAsDecimalMark != config.useCommaAsDecimalMark) {
+            setupDecimalSeparator()
+            updateWidgets()
+        }
+
         vibrateOnButtonPress = config.vibrateOnButtonPress
 
         val properPrimaryColor = getProperPrimaryColor()
@@ -117,6 +129,7 @@ class MainActivity : SimpleActivity(), Calculator {
     private fun storeStateVariables() {
         config.apply {
             storedTextColor = textColor
+            storedUseCommaAsDecimalMark = useCommaAsDecimalMark
         }
     }
 
@@ -186,4 +199,30 @@ class MainActivity : SimpleActivity(), Calculator {
     override fun showNewFormula(value: String, context: Context) {
         formula.text = value
     }
+
+    private fun setupDecimalSeparator() {
+        storedUseCommaAsDecimalMark = config.useCommaAsDecimalMark
+        if (storedUseCommaAsDecimalMark) {
+            decimalSeparator = COMMA
+            groupingSeparator = DOT
+        } else {
+            decimalSeparator = DOT
+            groupingSeparator = COMMA
+        }
+        calc.updateSeparators(decimalSeparator, groupingSeparator)
+        btn_decimal.text = decimalSeparator
+    }
+
+    private fun View.setVibratingOnClickListener(callback: (view: View) -> Unit) {
+        setOnClickListener {
+            callback(it)
+            checkHaptic(it)
+        }
+    }
+
+    private fun View.setOnClickOperation(operation: String) {
+        setVibratingOnClickListener {
+            calc.handleOperation(operation)
+        }
+    }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/activities/SettingsActivity.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/activities/SettingsActivity.kt
index 6d912c02..e12e9568 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/activities/SettingsActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/activities/SettingsActivity.kt
@@ -4,13 +4,17 @@ import android.content.Intent
 import android.os.Bundle
 import android.view.Menu
 import com.simplemobiletools.calculator.R
+import com.simplemobiletools.calculator.extensions.calculatorDB
 import com.simplemobiletools.calculator.extensions.config
+import com.simplemobiletools.calculator.extensions.updateWidgets
 import com.simplemobiletools.commons.extensions.*
 import com.simplemobiletools.commons.helpers.IS_CUSTOMIZING_COLORS
+import com.simplemobiletools.commons.helpers.ensureBackgroundThread
 import kotlinx.android.synthetic.main.activity_settings.*
 import java.util.*
 import kotlin.system.exitProcess
 
+
 class SettingsActivity : SimpleActivity() {
 
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -26,6 +30,7 @@ class SettingsActivity : SimpleActivity() {
         setupUseEnglish()
         setupVibrate()
         setupPreventPhoneFromSleeping()
+        setupUseCommaAsDecimalMark()
         setupCustomizeWidgetColors()
         updateTextColors(settings_scrollview)
 
@@ -94,6 +99,18 @@ class SettingsActivity : SimpleActivity() {
         }
     }
 
+    private fun setupUseCommaAsDecimalMark() {
+        settings_use_comma_as_decimal_mark.isChecked = config.useCommaAsDecimalMark
+        settings_use_comma_as_decimal_mark_holder.setOnClickListener {
+            settings_use_comma_as_decimal_mark.toggle()
+            config.useCommaAsDecimalMark = settings_use_comma_as_decimal_mark.isChecked
+            updateWidgets()
+            ensureBackgroundThread { 
+                applicationContext.calculatorDB.deleteHistory() 
+            }
+        }
+    }
+
     private fun setupCustomizeWidgetColors() {
         settings_customize_widget_colors_holder.setOnClickListener {
             Intent(this, WidgetConfigureActivity::class.java).apply {
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/extensions/Context.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/extensions/Context.kt
index a3b2b266..04a6efdd 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/extensions/Context.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/extensions/Context.kt
@@ -1,12 +1,16 @@
 package com.simplemobiletools.calculator.extensions
 
+import android.appwidget.AppWidgetManager
+import android.content.ComponentName
 import android.content.Context
+import android.content.Intent
 import android.view.ViewGroup
 import android.widget.Button
 import android.widget.TextView
-import com.simplemobiletools.calculator.helpers.Config
-import com.simplemobiletools.calculator.interfaces.CalculatorDao
 import com.simplemobiletools.calculator.databases.CalculatorDatabase
+import com.simplemobiletools.calculator.helpers.Config
+import com.simplemobiletools.calculator.helpers.MyWidgetProvider
+import com.simplemobiletools.calculator.interfaces.CalculatorDao
 
 val Context.config: Config get() = Config.newInstance(applicationContext)
 
@@ -16,11 +20,23 @@ val Context.calculatorDB: CalculatorDao get() = CalculatorDatabase.getInstance(a
 fun Context.updateViewColors(viewGroup: ViewGroup, textColor: Int) {
     val cnt = viewGroup.childCount
     (0 until cnt).map { viewGroup.getChildAt(it) }
-            .forEach {
-                when (it) {
-                    is TextView -> it.setTextColor(textColor)
-                    is Button -> it.setTextColor(textColor)
-                    is ViewGroup -> updateViewColors(it, textColor)
-                }
+        .forEach {
+            when (it) {
+                is TextView -> it.setTextColor(textColor)
+                is Button -> it.setTextColor(textColor)
+                is ViewGroup -> updateViewColors(it, textColor)
             }
+        }
+}
+
+fun Context.updateWidgets() {
+    val widgetIDs = AppWidgetManager.getInstance(applicationContext)?.getAppWidgetIds(ComponentName(applicationContext, MyWidgetProvider::class.java))
+        ?: return
+    if (widgetIDs.isNotEmpty()) {
+        Intent(applicationContext, MyWidgetProvider::class.java).apply {
+            action = AppWidgetManager.ACTION_APPWIDGET_UPDATE
+            putExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS, widgetIDs)
+            sendBroadcast(this)
+        }
+    }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/CalculatorImpl.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/CalculatorImpl.kt
index 9ae38448..d04cdbd3 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/CalculatorImpl.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/CalculatorImpl.kt
@@ -8,7 +8,12 @@ import com.simplemobiletools.commons.extensions.toast
 import net.objecthunter.exp4j.ExpressionBuilder
 import java.math.BigDecimal
 
-class CalculatorImpl(calculator: Calculator, private val context: Context) {
+class CalculatorImpl(
+    calculator: Calculator,
+    private val context: Context,
+    private var decimalSeparator: String = DOT,
+    private var groupingSeparator: String = COMMA
+) {
     private var callback: Calculator? = calculator
 
     private var baseValue = 0.0
@@ -20,6 +25,10 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
     private val operationsRegex = "[-+×÷^%√]".toPattern()
     private val numbersRegex = "[^0-9,.]".toRegex()
 
+    private val formatter = NumberFormatHelper(
+        decimalSeparator = decimalSeparator, groupingSeparator = groupingSeparator
+    )
+
     init {
         showNewResult("0")
     }
@@ -35,21 +44,21 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
     }
 
     private fun zeroClicked() {
-        val valueToCheck = inputDisplayedFormula.trimStart('-').replace(",", "")
+        val valueToCheck = inputDisplayedFormula.trimStart('-').removeGroupSeparator()
         val value = valueToCheck.substring(valueToCheck.indexOfAny(operations) + 1)
-        if (value != "0" || value.contains(".")) {
+        if (value != "0" || value.contains(decimalSeparator)) {
             addDigit(0)
         }
     }
 
     private fun decimalClicked() {
-        val valueToCheck = inputDisplayedFormula.trimStart('-').replace(",", "")
+        val valueToCheck = inputDisplayedFormula.trimStart('-').replace(groupingSeparator, "")
         val value = valueToCheck.substring(valueToCheck.indexOfAny(operations) + 1)
-        if (!value.contains(".")) {
+        if (!value.contains(decimalSeparator)) {
             when {
-                value == "0" && !valueToCheck.contains(operationsRegex.toRegex()) -> inputDisplayedFormula = "0."
-                value == "" -> inputDisplayedFormula += "0."
-                else -> inputDisplayedFormula += "."
+                value == "0" && !valueToCheck.contains(operationsRegex.toRegex()) -> inputDisplayedFormula = "0$decimalSeparator"
+                value == "" -> inputDisplayedFormula += "0$decimalSeparator"
+                else -> inputDisplayedFormula += decimalSeparator
             }
         }
 
@@ -60,10 +69,13 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
     private fun addThousandsDelimiter() {
         val valuesToCheck = numbersRegex.split(inputDisplayedFormula).filter { it.trim().isNotEmpty() }
         valuesToCheck.forEach {
-            var newString = Formatter.addGroupingSeparators(it)
+            var newString = formatter.addGroupingSeparators(it)
+
             // allow writing numbers like 0.003
-            if (it.contains(".")) {
-                newString = newString.substringBefore(".") + ".${it.substringAfter(".")}"
+            if (it.contains(decimalSeparator)) {
+                val firstPart = newString.substringBefore(decimalSeparator)
+                val lastPart = it.substringAfter(decimalSeparator)
+                newString = "$firstPart$decimalSeparator$lastPart"
             }
 
             inputDisplayedFormula = inputDisplayedFormula.replace(it, newString)
@@ -86,7 +98,7 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
         }
 
         val lastChar = inputDisplayedFormula.last().toString()
-        if (lastChar == ".") {
+        if (lastChar == decimalSeparator) {
             inputDisplayedFormula = inputDisplayedFormula.dropLast(1)
         } else if (operations.contains(lastChar)) {
             inputDisplayedFormula = inputDisplayedFormula.dropLast(1)
@@ -137,7 +149,7 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
             return false
         }
 
-        if (!inputDisplayedFormula.trimStart('-').any { it.toString() in operations } && inputDisplayedFormula.replace(",", "").toDouble() != 0.0) {
+        if (!inputDisplayedFormula.trimStart('-').any { it.toString() in operations } && inputDisplayedFormula.removeGroupSeparator().toDouble() != 0.0) {
             inputDisplayedFormula = if (inputDisplayedFormula.first() == '-') {
                 inputDisplayedFormula.substring(1)
             } else {
@@ -185,7 +197,7 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
     }
 
     private fun getSecondValue(): Double {
-        val valueToCheck = inputDisplayedFormula.trimStart('-').replace(",", "")
+        val valueToCheck = inputDisplayedFormula.trimStart('-').removeGroupSeparator()
         var value = valueToCheck.substring(valueToCheck.indexOfAny(operations) + 1)
         if (value == "") {
             value = "0"
@@ -205,23 +217,28 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
         }
 
         if (lastKey != EQUALS) {
-            val valueToCheck = inputDisplayedFormula.trimStart('-').replace(",", "")
+            val valueToCheck = inputDisplayedFormula.trimStart('-').removeGroupSeparator()
             val parts = valueToCheck.split(operationsRegex).filter { it != "" }
             if (parts.isEmpty()) {
                 return
             }
 
-            baseValue = Formatter.stringToDouble(parts.first())
+            baseValue = parts.first().toDouble()
             if (inputDisplayedFormula.startsWith("-")) {
                 baseValue *= -1
             }
 
-            secondValue = parts.getOrNull(1)?.replace(",", "")?.toDouble() ?: secondValue
+            secondValue = parts.getOrNull(1)?.toDouble() ?: secondValue
         }
 
         if (lastOperation != "") {
             val sign = getSign(lastOperation)
-            val expression = "${baseValue.format()}$sign${secondValue.format()}".replace("√", "sqrt").replace("×", "*").replace("÷", "/")
+            val formattedBaseValue = baseValue.format().removeGroupSeparator()
+            val formatterSecondValue = secondValue.format().removeGroupSeparator()
+            val expression = "$formattedBaseValue$sign$formatterSecondValue"
+                .replace("√", "sqrt")
+                .replace("×", "*")
+                .replace("÷", "/")
 
             try {
                 if (sign == "÷" && secondValue == 0.0) {
@@ -229,16 +246,11 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
                     return
                 }
 
-                if (sign == "%") {
-                    val second = secondValue / 100f
-                    "${baseValue.format()}*${second.format()}".replace("√", "sqrt").replace("×", "*").replace("÷", "/")
-                }
-
                 // handle percents manually, it doesn't seem to be possible via net.objecthunter:exp4j. "%" is used only for modulo there
                 // handle cases like 10%200 here
                 val result = if (sign == "%") {
-                    val second = secondValue / 100f
-                    ExpressionBuilder("${baseValue.format().replace(",", "")}*${second.format()}").build().evaluate()
+                    val second = (secondValue / 100f).format().removeGroupSeparator()
+                    ExpressionBuilder("$formattedBaseValue*$second").build().evaluate()
                 } else {
                     // avoid Double rounding errors at expressions like 5250,74 + 14,98
                     if (sign == "+" || sign == "-") {
@@ -250,7 +262,7 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
                         }
                         bigDecimalResult.toDouble()
                     } else {
-                        ExpressionBuilder(expression.replace(",", "")).build().evaluate()
+                        ExpressionBuilder(expression).build().evaluate()
                     }
                 }
 
@@ -260,11 +272,14 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
                 }
 
                 showNewResult(result.format())
-                baseValue = result
-                val newFormula = expression.replace("sqrt", "√").replace("*", "×").replace("/", "÷")
-                HistoryHelper(context).insertOrUpdateHistoryEntry(History(null, newFormula, result.format(), System.currentTimeMillis()))
-                inputDisplayedFormula = result.format()
+                val newFormula = "${baseValue.format()}$sign${secondValue.format()}"
+                HistoryHelper(context).insertOrUpdateHistoryEntry(
+                    History(id = null, formula = newFormula, result = result.format(), timestamp = System.currentTimeMillis())
+                )
                 showNewFormula(newFormula)
+
+                inputDisplayedFormula = result.format()
+                baseValue = result
             } catch (e: Exception) {
                 context.toast(R.string.unknown_error_occurred)
             }
@@ -317,19 +332,13 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
             }
             val lastValue = newValue.last().toString()
             lastKey = when {
-                operations.contains(lastValue) -> {
-                    CLEAR
-                }
-                lastValue == "." -> {
-                    DECIMAL
-                }
-                else -> {
-                    DIGIT
-                }
+                operations.contains(lastValue) -> CLEAR
+                lastValue == decimalSeparator -> DECIMAL
+                else -> DIGIT
             }
         }
 
-        newValue = newValue.trimEnd(',')
+        newValue = newValue.trimEnd(groupingSeparator.single())
         inputDisplayedFormula = newValue
         addThousandsDelimiter()
         showNewResult(inputDisplayedFormula)
@@ -391,4 +400,19 @@ class CalculatorImpl(calculator: Calculator, private val context: Context) {
         addThousandsDelimiter()
         showNewResult(inputDisplayedFormula)
     }
+
+    fun updateSeparators(decimalSeparator: String, groupingSeparator: String) {
+        if (this.decimalSeparator != decimalSeparator || this.groupingSeparator != groupingSeparator) {
+            this.decimalSeparator = decimalSeparator
+            this.groupingSeparator = groupingSeparator
+            formatter.decimalSeparator = decimalSeparator
+            formatter.groupingSeparator = groupingSeparator
+            // future: maybe update the formulas with new separators instead of resetting the whole thing
+            handleReset()
+        }
+    }
+
+    private fun Double.format() = formatter.doubleToString(this)
+
+    private fun String.removeGroupSeparator() = formatter.removeGroupingSeparator(this)
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Config.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Config.kt
index f9c286a0..004a3863 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Config.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Config.kt
@@ -7,4 +7,8 @@ class Config(context: Context) : BaseConfig(context) {
     companion object {
         fun newInstance(context: Context) = Config(context)
     }
+
+    var useCommaAsDecimalMark: Boolean
+        get() = prefs.getBoolean(USE_COMMA_AS_DECIMAL_MARK, false)
+        set(useCommaAsDecimalMark) = prefs.edit().putBoolean(USE_COMMA_AS_DECIMAL_MARK, useCommaAsDecimalMark).apply()
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Constants.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Constants.kt
index 8e8af427..a00ac851 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Constants.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Constants.kt
@@ -24,3 +24,9 @@ const val SIX = "six"
 const val SEVEN = "seven"
 const val EIGHT = "eight"
 const val NINE = "nine"
+
+const val DOT = "."
+const val COMMA = ","
+
+// shared prefs
+const val USE_COMMA_AS_DECIMAL_MARK = "use_comma_as_decimal_mark"
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Formatter.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Formatter.kt
deleted file mode 100644
index 6827f083..00000000
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/Formatter.kt
+++ /dev/null
@@ -1,25 +0,0 @@
-package com.simplemobiletools.calculator.helpers
-
-import java.text.DecimalFormat
-import java.text.DecimalFormatSymbols
-import java.util.*
-
-object Formatter {
-    fun doubleToString(d: Double): String {
-        val symbols = DecimalFormatSymbols(Locale.US)
-        symbols.decimalSeparator = '.'
-        symbols.groupingSeparator = ','
-
-        val formatter = DecimalFormat()
-        formatter.maximumFractionDigits = 12
-        formatter.decimalFormatSymbols = symbols
-        formatter.isGroupingUsed = true
-        return formatter.format(d)
-    }
-
-    fun stringToDouble(str: String) = str.replace(",", "").toDouble()
-
-    fun addGroupingSeparators(str: String) = doubleToString(stringToDouble(str))
-}
-
-fun Double.format(): String = Formatter.doubleToString(this)
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/MyWidgetProvider.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/MyWidgetProvider.kt
index ca1cadbf..45cdd3e1 100644
--- a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/MyWidgetProvider.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/MyWidgetProvider.kt
@@ -17,6 +17,9 @@ import com.simplemobiletools.commons.extensions.setText
 class MyWidgetProvider : AppWidgetProvider(), Calculator {
     companion object {
         private var calc: CalculatorImpl? = null
+        private var storedUseCommaAsDecimalMark = false
+        private var decimalSeparator = DOT
+        private var groupingSeparator = COMMA
     }
 
     override fun onUpdate(context: Context, appWidgetManager: AppWidgetManager, appWidgetIds: IntArray) {
@@ -53,6 +56,7 @@ class MyWidgetProvider : AppWidgetProvider(), Calculator {
             views.applyColorFilter(R.id.widget_background, config.widgetBgColor)
 
             updateTextColors(views, config.widgetTextColor)
+            setupDecimalSeparator(views, config.useCommaAsDecimalMark)
             appWidgetManager.updateAppWidget(it, views)
         }
     }
@@ -97,7 +101,7 @@ class MyWidgetProvider : AppWidgetProvider(), Calculator {
 
     private fun myAction(action: String, context: Context) {
         if (calc == null) {
-            calc = CalculatorImpl(this, context)
+            calc = CalculatorImpl(this, context, decimalSeparator, groupingSeparator)
         }
 
         when (action) {
@@ -141,4 +145,17 @@ class MyWidgetProvider : AppWidgetProvider(), Calculator {
         super.onDeleted(context, appWidgetIds)
         calc = null
     }
+
+    private fun setupDecimalSeparator(views: RemoteViews, useCommaAsDecimalMark: Boolean) {
+        storedUseCommaAsDecimalMark = useCommaAsDecimalMark
+        if (storedUseCommaAsDecimalMark) {
+            decimalSeparator = COMMA
+            groupingSeparator = DOT
+        } else {
+            decimalSeparator = DOT
+            groupingSeparator = COMMA
+        }
+        calc?.updateSeparators(decimalSeparator, groupingSeparator)
+        views.setTextViewText(R.id.btn_decimal, decimalSeparator)
+    }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/NumberFormatHelper.kt b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/NumberFormatHelper.kt
new file mode 100644
index 00000000..eb8d3e9f
--- /dev/null
+++ b/app/src/main/kotlin/com/simplemobiletools/calculator/helpers/NumberFormatHelper.kt
@@ -0,0 +1,31 @@
+package com.simplemobiletools.calculator.helpers
+
+import java.text.DecimalFormat
+import java.text.DecimalFormatSymbols
+import java.util.*
+
+class NumberFormatHelper(
+    var decimalSeparator: String = DOT,
+    var groupingSeparator: String = COMMA
+) {
+
+    fun doubleToString(d: Double): String {
+        val symbols = DecimalFormatSymbols(Locale.US)
+        symbols.decimalSeparator = decimalSeparator.single()
+        symbols.groupingSeparator = groupingSeparator.single()
+
+        val formatter = DecimalFormat()
+        formatter.maximumFractionDigits = 12
+        formatter.decimalFormatSymbols = symbols
+        formatter.isGroupingUsed = true
+        return formatter.format(d)
+    }
+
+    fun addGroupingSeparators(str: String): String {
+        return doubleToString(removeGroupingSeparator(str).toDouble())
+    }
+
+    fun removeGroupingSeparator(str: String): String {
+        return str.replace(groupingSeparator, "").replace(decimalSeparator, DOT)
+    }
+}
diff --git a/app/src/main/res/layout/activity_settings.xml b/app/src/main/res/layout/activity_settings.xml
index 87e7e4f7..cfd6fb4b 100644
--- a/app/src/main/res/layout/activity_settings.xml
+++ b/app/src/main/res/layout/activity_settings.xml
@@ -126,7 +126,7 @@
                 style="@style/SettingsHolderCheckboxStyle"
                 android:layout_width="match_parent"
                 android:layout_height="wrap_content"
-                android:background="@drawable/ripple_bottom_corners">
+                android:background="@drawable/ripple_background">
 
                 <com.simplemobiletools.commons.views.MyAppCompatCheckbox
                     android:id="@+id/settings_prevent_phone_from_sleeping"
@@ -136,6 +136,22 @@
                     android:text="@string/prevent_phone_from_sleeping" />
 
             </RelativeLayout>
+
+            <RelativeLayout
+                android:id="@+id/settings_use_comma_as_decimal_mark_holder"
+                style="@style/SettingsHolderCheckboxStyle"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:background="@drawable/ripple_bottom_corners">
+
+                <com.simplemobiletools.commons.views.MyAppCompatCheckbox
+                    android:id="@+id/settings_use_comma_as_decimal_mark"
+                    style="@style/SettingsCheckboxStyle"
+                    android:layout_width="match_parent"
+                    android:layout_height="wrap_content"
+                    android:text="@string/use_comma_as_decimal_mark" />
+
+            </RelativeLayout>
         </LinearLayout>
     </LinearLayout>
 </ScrollView>