diff --git a/tests/test_calculator.py b/tests/test_calculator.py
index d90f99d..94fa811 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, average, clamp, clamp_to_byte, median, subtract, variance
+from typosaurus_sandbox.domain.calculator import add, average, clamp, clamp_to_byte, median, percentage, subtract, variance
 
 
 class TestAddFunction(unittest.TestCase):
@@ -181,3 +181,46 @@ class TestVarianceFunction(unittest.TestCase):
     def test_tuple_input_returns_variance(self) -> None:
         self.assertEqual(variance((1, 2, 3, 4, 5)), 2.0)
 
+
+class TestPercentageFunction(unittest.TestCase):
+
+    def test_half_returns_50(self) -> None:
+        self.assertEqual(percentage(50, 100), 50.0)
+
+    def test_quarter_returns_25(self) -> None:
+        self.assertEqual(percentage(25, 100), 25.0)
+
+    def test_zero_value_returns_zero(self) -> None:
+        self.assertEqual(percentage(0, 100), 0.0)
+
+    def test_value_exceeds_total(self) -> None:
+        self.assertEqual(percentage(150, 100), 150.0)
+
+    def test_negative_value(self) -> None:
+        self.assertEqual(percentage(-50, 100), -50.0)
+
+    def test_negative_total(self) -> None:
+        self.assertEqual(percentage(50, -100), -50.0)
+
+    def test_both_negative(self) -> None:
+        self.assertEqual(percentage(-50, -100), 50.0)
+
+    def test_float_inputs(self) -> None:
+        result = percentage(33.0, 100.0)
+        self.assertAlmostEqual(result, 33.0)
+
+    def test_total_zero_raises_value_error(self) -> None:
+        with self.assertRaises(ValueError):
+            percentage(50, 0)
+
+    def test_total_zero_float_raises_value_error(self) -> None:
+        with self.assertRaises(ValueError):
+            percentage(50.0, 0.0)
+
+    def test_integer_inputs_return_float(self) -> None:
+        result = percentage(1, 4)
+        self.assertIsInstance(result, float)
+        self.assertEqual(result, 25.0)
+
+
+