diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 0a97a015..4709800b 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -380,6 +380,7 @@ list(APPEND SOURCE_FILES
         displayapp/screens/Metronome.cpp
         displayapp/screens/Motion.cpp
         displayapp/screens/Weather.cpp
+        displayapp/screens/Calculator.cpp
         displayapp/screens/FirmwareValidation.cpp
         displayapp/screens/ApplicationList.cpp
         displayapp/screens/Notifications.cpp
diff --git a/src/displayapp/DisplayApp.cpp b/src/displayapp/DisplayApp.cpp
index ff43bb81..749d8dee 100644
--- a/src/displayapp/DisplayApp.cpp
+++ b/src/displayapp/DisplayApp.cpp
@@ -30,6 +30,7 @@
 #include "displayapp/screens/Weather.h"
 #include "displayapp/screens/PassKey.h"
 #include "displayapp/screens/Error.h"
+#include "displayapp/screens/Calculator.h"
 
 #include "drivers/Cst816s.h"
 #include "drivers/St7789.h"
diff --git a/src/displayapp/apps/Apps.h.in b/src/displayapp/apps/Apps.h.in
index 2104a267..e697096a 100644
--- a/src/displayapp/apps/Apps.h.in
+++ b/src/displayapp/apps/Apps.h.in
@@ -26,6 +26,7 @@ namespace Pinetime {
       StopWatch,
       Metronome,
       Motion,
+      Calculator,
       Steps,
       Dice,
       Weather,
diff --git a/src/displayapp/apps/CMakeLists.txt b/src/displayapp/apps/CMakeLists.txt
index d7858760..33e54323 100644
--- a/src/displayapp/apps/CMakeLists.txt
+++ b/src/displayapp/apps/CMakeLists.txt
@@ -13,6 +13,7 @@ else ()
     set(DEFAULT_USER_APP_TYPES "${DEFAULT_USER_APP_TYPES}, Apps::Dice")
     set(DEFAULT_USER_APP_TYPES "${DEFAULT_USER_APP_TYPES}, Apps::Metronome")
     set(DEFAULT_USER_APP_TYPES "${DEFAULT_USER_APP_TYPES}, Apps::Navigation")
+    set(DEFAULT_USER_APP_TYPES "${DEFAULT_USER_APP_TYPES}, Apps::Calculator")
     set(DEFAULT_USER_APP_TYPES "${DEFAULT_USER_APP_TYPES}, Apps::Weather")
     #set(DEFAULT_USER_APP_TYPES "${DEFAULT_USER_APP_TYPES}, Apps::Motion")
     set(USERAPP_TYPES "${DEFAULT_USER_APP_TYPES}" CACHE STRING "List of user apps to build into the firmware")
diff --git a/src/displayapp/fonts/fonts.json b/src/displayapp/fonts/fonts.json
index 41c383c0..152a42e9 100644
--- a/src/displayapp/fonts/fonts.json
+++ b/src/displayapp/fonts/fonts.json
@@ -7,7 +7,7 @@
          },
          {
             "file": "FontAwesome5-Solid+Brands+Regular.woff",
-            "range": "0xf294, 0xf242, 0xf54b, 0xf21e, 0xf1e6, 0xf017, 0xf129, 0xf03a, 0xf185, 0xf560, 0xf001, 0xf3fd, 0xf1fc, 0xf45d, 0xf59f, 0xf5a0, 0xf027, 0xf028, 0xf6a9, 0xf04b, 0xf04c, 0xf048, 0xf051, 0xf095, 0xf3dd, 0xf04d, 0xf2f2, 0xf024, 0xf252, 0xf569, 0xf06e, 0xf015, 0xf00c, 0xf0f3, 0xf522, 0xf743"
+            "range": "0xf294, 0xf242, 0xf54b, 0xf21e, 0xf1e6, 0xf017, 0xf129, 0xf03a, 0xf185, 0xf560, 0xf001, 0xf3fd, 0xf1fc, 0xf45d, 0xf59f, 0xf5a0, 0xf027, 0xf028, 0xf6a9, 0xf04b, 0xf04c, 0xf048, 0xf051, 0xf095, 0xf3dd, 0xf04d, 0xf2f2, 0xf024, 0xf252, 0xf569, 0xf201, 0xf06e, 0xf015, 0xf00c, 0xf1ec, 0xf743, 0xf55a, 0xf0f3"
          }
       ],
       "bpp": 1,
diff --git a/src/displayapp/screens/Calculator.cpp b/src/displayapp/screens/Calculator.cpp
new file mode 100644
index 00000000..5f51b88d
--- /dev/null
+++ b/src/displayapp/screens/Calculator.cpp
@@ -0,0 +1,398 @@
+#include <cmath>
+#include <cinttypes>
+#include <libraries/log/nrf_log.h>
+#include "Calculator.h"
+#include "displayapp/InfiniTimeTheme.h"
+#include "Symbols.h"
+
+using namespace Pinetime::Applications::Screens;
+
+static void eventHandler(lv_obj_t* obj, lv_event_t event) {
+  auto app = static_cast<Calculator*>(obj->user_data);
+  app->OnButtonEvent(obj, event);
+}
+
+Calculator::~Calculator() {
+  lv_obj_clean(lv_scr_act());
+}
+
+constexpr char* const buttonMap[] = {
+  "7", "8", "9", Symbols::backspace, "\n", "4", "5", "6", "+ -", "\n", "1", "2", "3", "* /", "\n", "0", ".", "(-)", "=", ""};
+
+Calculator::Calculator() {
+  resultLabel = lv_label_create(lv_scr_act(), nullptr);
+  lv_label_set_long_mode(resultLabel, LV_LABEL_LONG_CROP);
+  lv_label_set_align(resultLabel, LV_LABEL_ALIGN_RIGHT);
+  lv_label_set_text_fmt(resultLabel, "%" PRId64, result);
+  lv_obj_set_size(resultLabel, 200, 20);
+  lv_obj_set_pos(resultLabel, 10, 5);
+
+  valueLabel = lv_label_create(lv_scr_act(), nullptr);
+  lv_label_set_long_mode(valueLabel, LV_LABEL_LONG_CROP);
+  lv_label_set_align(valueLabel, LV_LABEL_ALIGN_RIGHT);
+  lv_label_set_text_fmt(valueLabel, "%" PRId64, value);
+  lv_obj_set_size(valueLabel, 200, 20);
+  lv_obj_set_pos(valueLabel, 10, 35);
+
+  buttonMatrix = lv_btnmatrix_create(lv_scr_act(), nullptr);
+  buttonMatrix->user_data = this;
+  lv_obj_set_event_cb(buttonMatrix, eventHandler);
+  lv_btnmatrix_set_map(buttonMatrix, const_cast<const char**>(buttonMap));
+  lv_btnmatrix_set_one_check(buttonMatrix, true);
+  lv_obj_set_size(buttonMatrix, 238, 180);
+  lv_obj_set_style_local_bg_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_DEFAULT, Colors::bgAlt);
+  lv_obj_set_style_local_pad_inner(buttonMatrix, LV_BTNMATRIX_PART_BG, LV_STATE_DEFAULT, 1);
+  lv_obj_set_style_local_pad_top(buttonMatrix, LV_BTNMATRIX_PART_BG, LV_STATE_DEFAULT, 1);
+  lv_obj_set_style_local_pad_bottom(buttonMatrix, LV_BTNMATRIX_PART_BG, LV_STATE_DEFAULT, 1);
+  lv_obj_set_style_local_pad_left(buttonMatrix, LV_BTNMATRIX_PART_BG, LV_STATE_DEFAULT, 1);
+  lv_obj_set_style_local_pad_right(buttonMatrix, LV_BTNMATRIX_PART_BG, LV_STATE_DEFAULT, 1);
+  lv_obj_align(buttonMatrix, nullptr, LV_ALIGN_IN_BOTTOM_MID, 0, 0);
+
+  lv_obj_set_style_local_bg_opa(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, LV_OPA_COVER);
+  lv_obj_set_style_local_bg_grad_stop(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, 128);
+  lv_obj_set_style_local_bg_main_stop(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, 128);
+}
+
+void Calculator::OnButtonEvent(lv_obj_t* obj, lv_event_t event) {
+  if ((obj == buttonMatrix) && (event == LV_EVENT_PRESSED)) {
+    HandleInput();
+  }
+}
+
+void Calculator::HandleInput() {
+  const char* buttonText = lv_btnmatrix_get_active_btn_text(buttonMatrix);
+
+  if (buttonText == nullptr) {
+    return;
+  }
+
+  if ((equalSignPressed && (*buttonText != '=')) || (error != Error::None)) {
+    ResetInput();
+    UpdateOperation();
+  }
+
+  // we only compare the first char because it is enough
+  switch (*buttonText) {
+    case '0':
+    case '1':
+    case '2':
+    case '3':
+    case '4':
+    case '5':
+    case '6':
+    case '7':
+    case '8':
+    case '9': {
+      // *buttonText is the first char in buttonText
+      // "- '0'" results in the int value of the char
+      auto digit = (*buttonText) - '0';
+      auto sign = (value < 0) ? -1 : 1;
+
+      // if this is true, we already pressed the . button
+      if (offset < FIXED_POINT_OFFSET) {
+        value += sign * offset * digit;
+        offset /= 10;
+      } else if (value <= MAX_VALUE / 10) {
+        value *= 10;
+        value += sign * offset * digit;
+      }
+
+      NRF_LOG_INFO(". offset: %" PRId64, offset);
+      NRF_LOG_INFO(". value: %" PRId64, value);
+      NRF_LOG_INFO(". result: %" PRId64, result);
+    } break;
+
+    // unary minus
+    case '(':
+      value = -value;
+
+      NRF_LOG_INFO(". offset: %" PRId64, offset);
+      NRF_LOG_INFO(". value: %" PRId64, value);
+      NRF_LOG_INFO(". result: %" PRId64, result);
+
+      break;
+
+    case '.':
+      if (offset == FIXED_POINT_OFFSET) {
+        offset /= 10;
+      }
+
+      NRF_LOG_INFO(". offset: %" PRId64, offset);
+      NRF_LOG_INFO(". value: %" PRId64, value);
+      NRF_LOG_INFO(". result: %" PRId64, result);
+      break;
+
+    // for every operator we:
+    // - eval the current operator if value > FIXED_POINT_OFFSET
+    // - then set the new operator
+    // - + and - as well as * and / cycle on the same button
+    case '+':
+      if (value != 0) {
+        Eval();
+        ResetInput();
+      }
+
+      switch (operation) {
+        case '+':
+          operation = '-';
+          break;
+        case '-':
+          operation = ' ';
+          break;
+        default:
+          operation = '+';
+          break;
+      }
+      UpdateOperation();
+      break;
+
+    case '*':
+      if (value != 0) {
+        Eval();
+        ResetInput();
+      }
+
+      switch (operation) {
+        case '*':
+          operation = '/';
+          break;
+        case '/':
+          operation = ' ';
+          break;
+        default:
+          operation = '*';
+          break;
+      }
+      UpdateOperation();
+      break;
+
+    // this is a little hacky because it matches only the first char
+    case Symbols::backspace[0]:
+      if (value != 0) {
+        // delete one value digit
+        if (offset < FIXED_POINT_OFFSET) {
+          if (offset == 0) {
+            offset = 1;
+          } else {
+            offset *= 10;
+          }
+        } else {
+          value /= 10;
+        }
+        if (offset < FIXED_POINT_OFFSET) {
+          value -= value % (10 * offset);
+        } else {
+          value -= value % offset;
+        }
+      } else if (offset < FIXED_POINT_OFFSET) {
+        if (offset == 0) {
+          offset = 1;
+        } else {
+          offset *= 10;
+        }
+      } else {
+        // reset the result
+        result = 0;
+      }
+
+      NRF_LOG_INFO(". offset: %" PRId64, offset);
+      NRF_LOG_INFO(". value: %" PRId64, value);
+      NRF_LOG_INFO(". result: %" PRId64, result);
+
+      if (value == 0) {
+        operation = ' ';
+        UpdateOperation();
+      }
+      break;
+
+    case '=':
+      equalSignPressed = true;
+      Eval();
+      // If the operation is ' ' then we move the value to the result.
+      // We reset the input after this.
+      // This seems more convenient.
+      if (operation == ' ') {
+        ResetInput();
+      }
+
+      NRF_LOG_INFO(". offset: %" PRId64, offset);
+      NRF_LOG_INFO(". value: %" PRId64, value);
+      NRF_LOG_INFO(". result: %" PRId64, result);
+
+      break;
+  }
+
+  UpdateValueLabel();
+  UpdateResultLabel();
+}
+
+void Calculator::UpdateOperation() const {
+  switch (operation) {
+    case '+':
+      lv_obj_set_style_local_bg_grad_dir(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, LV_GRAD_DIR_HOR);
+      lv_obj_set_style_local_bg_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::deepOrange);
+      lv_obj_set_style_local_bg_grad_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::bgAlt);
+      lv_btnmatrix_set_btn_ctrl(buttonMatrix, 7, LV_BTNMATRIX_CTRL_CHECK_STATE);
+      break;
+    case '-':
+      lv_obj_set_style_local_bg_grad_dir(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, LV_GRAD_DIR_HOR);
+      lv_obj_set_style_local_bg_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::bgAlt);
+      lv_obj_set_style_local_bg_grad_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::deepOrange);
+      lv_btnmatrix_set_btn_ctrl(buttonMatrix, 7, LV_BTNMATRIX_CTRL_CHECK_STATE);
+      break;
+    case '*':
+      lv_obj_set_style_local_bg_grad_dir(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, LV_GRAD_DIR_HOR);
+      lv_obj_set_style_local_bg_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::deepOrange);
+      lv_obj_set_style_local_bg_grad_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::bgAlt);
+      lv_btnmatrix_set_btn_ctrl(buttonMatrix, 11, LV_BTNMATRIX_CTRL_CHECK_STATE);
+      break;
+    case '/':
+      lv_obj_set_style_local_bg_grad_dir(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, LV_GRAD_DIR_HOR);
+      lv_obj_set_style_local_bg_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::bgAlt);
+      lv_obj_set_style_local_bg_grad_color(buttonMatrix, LV_BTNMATRIX_PART_BTN, LV_STATE_CHECKED, Colors::deepOrange);
+      lv_btnmatrix_set_btn_ctrl(buttonMatrix, 11, LV_BTNMATRIX_CTRL_CHECK_STATE);
+      break;
+    default:
+      lv_btnmatrix_clear_btn_ctrl_all(buttonMatrix, LV_BTNMATRIX_CTRL_CHECK_STATE);
+      break;
+  }
+}
+
+void Calculator::ResetInput() {
+  value = 0;
+  offset = FIXED_POINT_OFFSET;
+  operation = ' ';
+  equalSignPressed = false;
+  error = Error::None;
+}
+
+void Calculator::UpdateResultLabel() const {
+  int64_t integer = result / FIXED_POINT_OFFSET;
+  int64_t remainder = result % FIXED_POINT_OFFSET;
+  bool negative = (remainder < 0);
+
+  if (remainder == 0) {
+    lv_label_set_text_fmt(resultLabel, "%" PRId64, integer);
+    return;
+  }
+
+  if (remainder < 0) {
+    remainder = -remainder;
+  }
+
+  uint8_t min_width = N_DECIMALS;
+
+  // cut "0"-digits on the right
+  while ((remainder > 0) && (remainder % 10 == 0)) {
+    remainder /= 10;
+    min_width--;
+  }
+
+  if ((integer == 0) && negative) {
+    lv_label_set_text_fmt(resultLabel, "-0.%0*" PRId64, min_width, remainder);
+  } else {
+    lv_label_set_text_fmt(resultLabel, "%" PRId64 ".%0*" PRId64, integer, min_width, remainder);
+  }
+}
+
+void Calculator::UpdateValueLabel() {
+  switch (error) {
+    case Error::TooLarge:
+      lv_label_set_text_static(valueLabel, "too large");
+      break;
+    case Error::ZeroDivision:
+      lv_label_set_text_static(valueLabel, "zero division");
+      break;
+    case Error::None:
+    default: {
+      int64_t integer = value / FIXED_POINT_OFFSET;
+      int64_t remainder = value % FIXED_POINT_OFFSET;
+      bool negative = (remainder < 0);
+
+      int64_t printRemainder = remainder < 0 ? -remainder : remainder;
+
+      uint8_t min_width = 0;
+      int64_t tmp_offset = offset;
+
+      if (tmp_offset == 0) {
+        tmp_offset = 1;
+        min_width = 1;
+      }
+      while (tmp_offset < FIXED_POINT_OFFSET) {
+        tmp_offset *= 10;
+        min_width++;
+      }
+      min_width--;
+
+      for (uint8_t i = min_width; i < N_DECIMALS; i++) {
+        printRemainder /= 10;
+      }
+
+      if ((integer == 0) && negative) {
+        lv_label_set_text_fmt(valueLabel, "-0.%0*" PRId64, min_width, printRemainder);
+      } else if (offset == FIXED_POINT_OFFSET) {
+        lv_label_set_text_fmt(valueLabel, "%" PRId64, integer);
+      } else if ((offset == (FIXED_POINT_OFFSET / 10)) && (remainder == 0)) {
+        lv_label_set_text_fmt(valueLabel, "%" PRId64 ".", integer);
+      } else {
+        lv_label_set_text_fmt(valueLabel, "%" PRId64 ".%0*" PRId64, integer, min_width, printRemainder);
+      }
+    } break;
+  }
+}
+
+// update the result based on value and operation
+void Calculator::Eval() {
+  switch (operation) {
+    case ' ':
+      result = value;
+      break;
+
+    case '+':
+      // check for overflow
+      if (((result > 0) && (value > (MAX_VALUE - result))) || ((result < 0) && (value < (MIN_VALUE - result)))) {
+        error = Error::TooLarge;
+        break;
+      }
+
+      result += value;
+      break;
+    case '-':
+      // check for overflow
+      if (((result < 0) && (value > (MAX_VALUE + result))) || ((result > 0) && (value < (MIN_VALUE + result)))) {
+        error = Error::TooLarge;
+        break;
+      }
+
+      result -= value;
+      break;
+    case '*':
+      // check for overflow
+      // while dividing we eliminate the fixed point offset
+      // therefore we have to multiply it again for the comparison with value
+      // we also assume here that MAX_VALUE == -MIN_VALUE
+      if ((result != 0) && (std::abs(value) > (FIXED_POINT_OFFSET * (MAX_VALUE / std::abs(result))))) {
+        error = Error::TooLarge;
+        break;
+      }
+
+      result *= value;
+      // fixed point offset was multiplied too
+      result /= FIXED_POINT_OFFSET;
+      break;
+    case '/':
+      // check for zero division
+      if (value == 0) {
+        error = Error::ZeroDivision;
+        break;
+      }
+
+      // fixed point offset will be divided too
+      result *= FIXED_POINT_OFFSET;
+      result /= value;
+      break;
+
+    default:
+      break;
+  }
+}
diff --git a/src/displayapp/screens/Calculator.h b/src/displayapp/screens/Calculator.h
new file mode 100644
index 00000000..99d86e75
--- /dev/null
+++ b/src/displayapp/screens/Calculator.h
@@ -0,0 +1,81 @@
+#pragma once
+
+#include "displayapp/screens/Screen.h"
+#include "displayapp/apps/Apps.h"
+#include "displayapp/Controllers.h"
+#include "Symbols.h"
+
+namespace {
+  int64_t constexpr powi(int64_t base, uint8_t exponent) {
+    int64_t value = 1;
+    while (exponent) {
+      value *= base;
+      exponent--;
+    }
+    return value;
+  }
+}
+
+namespace Pinetime {
+  namespace Applications {
+    namespace Screens {
+      class Calculator : public Screen {
+      public:
+        ~Calculator() override;
+
+        Calculator();
+
+        void OnButtonEvent(lv_obj_t* obj, lv_event_t event);
+
+      private:
+        lv_obj_t* buttonMatrix {};
+        lv_obj_t* valueLabel {};
+        lv_obj_t* resultLabel {};
+
+        void Eval();
+        void ResetInput();
+        void HandleInput();
+        void UpdateValueLabel();
+        void UpdateResultLabel() const;
+        void UpdateOperation() const;
+
+        // change this if you want to change the number of decimals
+        static constexpr uint8_t N_DECIMALS = 3;
+        // this is the constant default offset
+        static constexpr int64_t FIXED_POINT_OFFSET = powi(10, N_DECIMALS);
+        // this is the current offset, may wary after pressing '.'
+        int64_t offset = FIXED_POINT_OFFSET;
+
+        // the screen can show 12 chars
+        // but two are needed for '.' and '-'
+        static constexpr uint8_t MAX_DIGITS = 12;
+        static constexpr int64_t MAX_VALUE = powi(10, MAX_DIGITS) - 1;
+        // this is assumed in the multiplication overflow!
+        static constexpr int64_t MIN_VALUE = -MAX_VALUE;
+
+        int64_t value = 0;
+        int64_t result = 0;
+        char operation = ' ';
+        bool equalSignPressed = false;
+
+        enum Error {
+          TooLarge,
+          ZeroDivision,
+          None,
+        };
+
+        Error error = Error::None;
+      };
+    }
+
+    template <>
+    struct AppTraits<Apps::Calculator> {
+      static constexpr Apps app = Apps::Calculator;
+      static constexpr const char* icon = Screens::Symbols::calculator;
+
+      static Screens::Screen* Create(AppControllers& /* controllers */) {
+        return new Screens::Calculator();
+      };
+    };
+  }
+}
diff --git a/src/displayapp/screens/Symbols.h b/src/displayapp/screens/Symbols.h
index bd958b28..40699b3d 100644
--- a/src/displayapp/screens/Symbols.h
+++ b/src/displayapp/screens/Symbols.h
@@ -39,6 +39,8 @@ namespace Pinetime {
         static constexpr const char* eye = "\xEF\x81\xAE";
         static constexpr const char* home = "\xEF\x80\x95";
         static constexpr const char* sleep = "\xEE\xBD\x84";
+        static constexpr const char* calculator = "\xEF\x87\xAC";
+        static constexpr const char* backspace = "\xEF\x95\x9A";
 
         // fontawesome_weathericons.c
         // static constexpr const char* sun = "\xEF\x86\x85";