diff --git a/src/typosaurus_sandbox/domain/calculator/__init__.py b/src/typosaurus_sandbox/domain/calculator/__init__.py
index 368ace9..e4dd0d5 100644
--- a/src/typosaurus_sandbox/domain/calculator/__init__.py
+++ b/src/typosaurus_sandbox/domain/calculator/__init__.py
@@ -1,6 +1,7 @@
 # retoor <retoor@molodetz.nl>
 
-from typosaurus_sandbox.domain.calculator.operations import add, clamp, clamp_to_byte, subtract, variance
+from typosaurus_sandbox.domain.calculator.operations import add, average, clamp, clamp_to_byte, percentage, subtract, variance
+
+__all__ = ["add", "average", "clamp", "clamp_to_byte", "percentage", "subtract", "variance"]
 
-__all__ = ["add", "subtract", "clamp", "clamp_to_byte", "variance"]
 
diff --git a/src/typosaurus_sandbox/domain/calculator/operations.py b/src/typosaurus_sandbox/domain/calculator/operations.py
index 173fdab..12f9426 100644
--- a/src/typosaurus_sandbox/domain/calculator/operations.py
+++ b/src/typosaurus_sandbox/domain/calculator/operations.py
@@ -1,6 +1,6 @@
 # retoor <retoor@molodetz.nl>
 
-from typing import Sequence
+from typing import Sequence, Union
 
 
 def add(left: int, right: int) -> int:
@@ -25,9 +25,21 @@ def clamp_to_byte(value: int) -> int:
     return max(0, min(255, value))
 
 
+def average(values: list[int | float]) -> float:
+    if not values:
+        raise ValueError
+    return sum(values) / len(values)
+
+
 def variance(values: Sequence[float]) -> float:
     if not values:
         raise ValueError
     mean = sum(values) / len(values)
     return sum((x - mean) ** 2 for x in values) / len(values)
 
+
+def percentage(value: Union[int, float], total: Union[int, float]) -> float:
+    if total == 0:
+        raise ValueError
+    return (value / total) * 100
+
diff --git a/tests/test_calculator.py b/tests/test_calculator.py
index d367009..a7d33b7 100644
--- a/tests/test_calculator.py
+++ b/tests/test_calculator.py
@@ -3,7 +3,7 @@
 import math
 import unittest
 
-from typosaurus_sandbox.domain.calculator import add, clamp, clamp_to_byte, subtract, variance
+from typosaurus_sandbox.domain.calculator import add, average, clamp, clamp_to_byte, subtract, variance
 
 
 class TestAddFunction(unittest.TestCase):
@@ -18,6 +18,28 @@ class TestAddFunction(unittest.TestCase):
         self.assertEqual(add(-3, 5), 2)
 
 
+class TestAverageFunction(unittest.TestCase):
+
+    def test_empty_sequence_raises_value_error(self) -> None:
+        with self.assertRaises(ValueError):
+            average([])
+
+    def test_single_element(self) -> None:
+        self.assertEqual(average([5]), 5.0)
+
+    def test_positive_values(self) -> None:
+        self.assertEqual(average([1, 2, 3, 4, 5]), 3.0)
+
+    def test_negative_values(self) -> None:
+        self.assertEqual(average([-10, -20, -30]), -20.0)
+
+    def test_mixed_positive_and_negative(self) -> None:
+        self.assertEqual(average([-5, 0, 5]), 0.0)
+
+    def test_float_values(self) -> None:
+        self.assertEqual(average([1.5, 2.5, 3.0]), 7.0 / 3.0)
+
+
 class TestSubtractFunction(unittest.TestCase):
 
     def test_subtract_positive(self) -> None: