diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1aa2480..175c5aa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@
 - Added `All` and `Any` for `Span<T>` and `ReadOnlySpan<T>`, mimicking the corresponding methods in `System.Linq`
 - Added time-related extension methods (`Ticks`, `Milliseconds`, `Seconds`, `Minutes`, `Hours`, `Days`, and `Weeks`) to all built-in numeric types
 - Added `TimeSpan.Ago()` and `TimeSpan.FromNow()`
+- Added `Factorial` extension method for built-in numeric types
 - Added `FileInfo.GetHash<T>()`
 - Added `FileInfo.TryWriteHash<T>(Span<byte>, out int)`
 - Added `IEnumerable<TSource>.Product()` and `IEnumerable<TSource>.Product<TResult>(Func<TSource>, TResult)` for all built-in numeric types, computing the product of all (transformed) elements
diff --git a/X10D.Tests/src/Math/ByteTests.cs b/X10D.Tests/src/Math/ByteTests.cs
new file mode 100644
index 0000000..41bf551
--- /dev/null
+++ b/X10D.Tests/src/Math/ByteTests.cs
@@ -0,0 +1,24 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+public class ByteTests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1L, ((byte)0).Factorial());
+        Assert.AreEqual(1L, ((byte)1).Factorial());
+        Assert.AreEqual(2L, ((byte)2).Factorial());
+        Assert.AreEqual(6L, ((byte)3).Factorial());
+        Assert.AreEqual(24L, ((byte)4).Factorial());
+        Assert.AreEqual(120L, ((byte)5).Factorial());
+        Assert.AreEqual(720L, ((byte)6).Factorial());
+        Assert.AreEqual(5040L, ((byte)7).Factorial());
+        Assert.AreEqual(40320L, ((byte)8).Factorial());
+        Assert.AreEqual(362880L, ((byte)9).Factorial());
+        Assert.AreEqual(3628800L, ((byte)10).Factorial());
+    }
+}
diff --git a/X10D.Tests/src/Math/Int16Tests.cs b/X10D.Tests/src/Math/Int16Tests.cs
new file mode 100644
index 0000000..6a31d3b
--- /dev/null
+++ b/X10D.Tests/src/Math/Int16Tests.cs
@@ -0,0 +1,30 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+public class Int16Tests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1L, ((short)0).Factorial());
+        Assert.AreEqual(1L, ((short)1).Factorial());
+        Assert.AreEqual(2L, ((short)2).Factorial());
+        Assert.AreEqual(6L, ((short)3).Factorial());
+        Assert.AreEqual(24L, ((short)4).Factorial());
+        Assert.AreEqual(120L, ((short)5).Factorial());
+        Assert.AreEqual(720L, ((short)6).Factorial());
+        Assert.AreEqual(5040L, ((short)7).Factorial());
+        Assert.AreEqual(40320L, ((short)8).Factorial());
+        Assert.AreEqual(362880L, ((short)9).Factorial());
+        Assert.AreEqual(3628800L, ((short)10).Factorial());
+    }
+
+    [TestMethod]
+    public void NegativeFactorialShouldThrow()
+    {
+        Assert.ThrowsException<ArithmeticException>(() => ((short)-1).Factorial());
+    }
+}
diff --git a/X10D.Tests/src/Math/Int32Tests.cs b/X10D.Tests/src/Math/Int32Tests.cs
new file mode 100644
index 0000000..c358d7a
--- /dev/null
+++ b/X10D.Tests/src/Math/Int32Tests.cs
@@ -0,0 +1,30 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+public class Int32Tests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1L, 0.Factorial());
+        Assert.AreEqual(1L, 1.Factorial());
+        Assert.AreEqual(2L, 2.Factorial());
+        Assert.AreEqual(6L, 3.Factorial());
+        Assert.AreEqual(24L, 4.Factorial());
+        Assert.AreEqual(120L, 5.Factorial());
+        Assert.AreEqual(720L, 6.Factorial());
+        Assert.AreEqual(5040L, 7.Factorial());
+        Assert.AreEqual(40320L, 8.Factorial());
+        Assert.AreEqual(362880L, 9.Factorial());
+        Assert.AreEqual(3628800L, 10.Factorial());
+    }
+
+    [TestMethod]
+    public void NegativeFactorialShouldThrow()
+    {
+        Assert.ThrowsException<ArithmeticException>(() => (-1).Factorial());
+    }
+}
diff --git a/X10D.Tests/src/Math/Int64Tests.cs b/X10D.Tests/src/Math/Int64Tests.cs
new file mode 100644
index 0000000..a1b21af
--- /dev/null
+++ b/X10D.Tests/src/Math/Int64Tests.cs
@@ -0,0 +1,30 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+public class Int64Tests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1L, 0L.Factorial());
+        Assert.AreEqual(1L, 1L.Factorial());
+        Assert.AreEqual(2L, 2L.Factorial());
+        Assert.AreEqual(6L, 3L.Factorial());
+        Assert.AreEqual(24L, 4L.Factorial());
+        Assert.AreEqual(120L, 5L.Factorial());
+        Assert.AreEqual(720L, 6L.Factorial());
+        Assert.AreEqual(5040L, 7L.Factorial());
+        Assert.AreEqual(40320L, 8L.Factorial());
+        Assert.AreEqual(362880L, 9L.Factorial());
+        Assert.AreEqual(3628800L, 10L.Factorial());
+    }
+
+    [TestMethod]
+    public void NegativeFactorialShouldThrow()
+    {
+        Assert.ThrowsException<ArithmeticException>(() => (-1L).Factorial());
+    }
+}
diff --git a/X10D.Tests/src/Math/SByteTests.cs b/X10D.Tests/src/Math/SByteTests.cs
new file mode 100644
index 0000000..c5279bb
--- /dev/null
+++ b/X10D.Tests/src/Math/SByteTests.cs
@@ -0,0 +1,31 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+[CLSCompliant(false)]
+public class SByteTests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1L, ((sbyte)0).Factorial());
+        Assert.AreEqual(1L, ((sbyte)1).Factorial());
+        Assert.AreEqual(2L, ((sbyte)2).Factorial());
+        Assert.AreEqual(6L, ((sbyte)3).Factorial());
+        Assert.AreEqual(24L, ((sbyte)4).Factorial());
+        Assert.AreEqual(120L, ((sbyte)5).Factorial());
+        Assert.AreEqual(720L, ((sbyte)6).Factorial());
+        Assert.AreEqual(5040L, ((sbyte)7).Factorial());
+        Assert.AreEqual(40320L, ((sbyte)8).Factorial());
+        Assert.AreEqual(362880L, ((sbyte)9).Factorial());
+        Assert.AreEqual(3628800L, ((sbyte)10).Factorial());
+    }
+
+    [TestMethod]
+    public void NegativeFactorialShouldThrow()
+    {
+        Assert.ThrowsException<ArithmeticException>(() => ((sbyte)-1).Factorial());
+    }
+}
diff --git a/X10D.Tests/src/Math/UInt16Tests.cs b/X10D.Tests/src/Math/UInt16Tests.cs
new file mode 100644
index 0000000..27619e9
--- /dev/null
+++ b/X10D.Tests/src/Math/UInt16Tests.cs
@@ -0,0 +1,25 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+[CLSCompliant(false)]
+public class UInt16Tests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1UL, ((ushort)0).Factorial());
+        Assert.AreEqual(1UL, ((ushort)1).Factorial());
+        Assert.AreEqual(2UL, ((ushort)2).Factorial());
+        Assert.AreEqual(6UL, ((ushort)3).Factorial());
+        Assert.AreEqual(24UL, ((ushort)4).Factorial());
+        Assert.AreEqual(120UL, ((ushort)5).Factorial());
+        Assert.AreEqual(720UL, ((ushort)6).Factorial());
+        Assert.AreEqual(5040UL, ((ushort)7).Factorial());
+        Assert.AreEqual(40320UL, ((ushort)8).Factorial());
+        Assert.AreEqual(362880UL, ((ushort)9).Factorial());
+        Assert.AreEqual(3628800UL, ((ushort)10).Factorial());
+    }
+}
diff --git a/X10D.Tests/src/Math/UInt32Tests.cs b/X10D.Tests/src/Math/UInt32Tests.cs
new file mode 100644
index 0000000..dc0fbf0
--- /dev/null
+++ b/X10D.Tests/src/Math/UInt32Tests.cs
@@ -0,0 +1,25 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+[CLSCompliant(false)]
+public class UInt32Tests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1UL, 0U.Factorial());
+        Assert.AreEqual(1UL, 1U.Factorial());
+        Assert.AreEqual(2UL, 2U.Factorial());
+        Assert.AreEqual(6UL, 3U.Factorial());
+        Assert.AreEqual(24UL, 4U.Factorial());
+        Assert.AreEqual(120UL, 5U.Factorial());
+        Assert.AreEqual(720UL, 6U.Factorial());
+        Assert.AreEqual(5040UL, 7U.Factorial());
+        Assert.AreEqual(40320UL, 8U.Factorial());
+        Assert.AreEqual(362880UL, 9U.Factorial());
+        Assert.AreEqual(3628800UL, 10U.Factorial());
+    }
+}
diff --git a/X10D.Tests/src/Math/UInt64Tests.cs b/X10D.Tests/src/Math/UInt64Tests.cs
new file mode 100644
index 0000000..0e02a77
--- /dev/null
+++ b/X10D.Tests/src/Math/UInt64Tests.cs
@@ -0,0 +1,25 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Math;
+
+namespace X10D.Tests.Math;
+
+[TestClass]
+[CLSCompliant(false)]
+public class UInt64Tests
+{
+    [TestMethod]
+    public void FactorialShouldBeCorrect()
+    {
+        Assert.AreEqual(1UL, 0UL.Factorial());
+        Assert.AreEqual(1UL, 1UL.Factorial());
+        Assert.AreEqual(2UL, 2UL.Factorial());
+        Assert.AreEqual(6UL, 3UL.Factorial());
+        Assert.AreEqual(24UL, 4UL.Factorial());
+        Assert.AreEqual(120UL, 5UL.Factorial());
+        Assert.AreEqual(720UL, 6UL.Factorial());
+        Assert.AreEqual(5040UL, 7UL.Factorial());
+        Assert.AreEqual(40320UL, 8UL.Factorial());
+        Assert.AreEqual(362880UL, 9UL.Factorial());
+        Assert.AreEqual(3628800UL, 10UL.Factorial());
+    }
+}
diff --git a/X10D/src/Math/ByteExtensions.cs b/X10D/src/Math/ByteExtensions.cs
new file mode 100644
index 0000000..fdbd177
--- /dev/null
+++ b/X10D/src/Math/ByteExtensions.cs
@@ -0,0 +1,28 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="byte" />.
+/// </summary>
+public static class ByteExtensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 8-bit unsigned integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    public static long Factorial(this byte value)
+    {
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1L;
+        for (byte i = 1; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}
diff --git a/X10D/src/Math/Int16Extensions.cs b/X10D/src/Math/Int16Extensions.cs
new file mode 100644
index 0000000..620ce0f
--- /dev/null
+++ b/X10D/src/Math/Int16Extensions.cs
@@ -0,0 +1,34 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="short" />.
+/// </summary>
+public static class Int16Extensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 16-bit signed integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    /// <exception cref="ArithmeticException"><paramref name="value" /> is less than 0.</exception>
+    public static long Factorial(this short value)
+    {
+        if (value < 0)
+        {
+            throw new ArithmeticException(nameof(value));
+        }
+
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1L;
+        for (short i = 1; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}
diff --git a/X10D/src/Math/Int32Extensions.cs b/X10D/src/Math/Int32Extensions.cs
new file mode 100644
index 0000000..bc73e36
--- /dev/null
+++ b/X10D/src/Math/Int32Extensions.cs
@@ -0,0 +1,34 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="int" />.
+/// </summary>
+public static class Int32Extensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 32-bit signed integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    /// <exception cref="ArithmeticException"><paramref name="value" /> is less than 0.</exception>
+    public static long Factorial(this int value)
+    {
+        if (value < 0)
+        {
+            throw new ArithmeticException(nameof(value));
+        }
+
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1L;
+        for (var i = 1; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}
diff --git a/X10D/src/Math/Int64Extensions.cs b/X10D/src/Math/Int64Extensions.cs
new file mode 100644
index 0000000..696e037
--- /dev/null
+++ b/X10D/src/Math/Int64Extensions.cs
@@ -0,0 +1,34 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="long" />.
+/// </summary>
+public static class Int64Extensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 64-bit signed integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    /// <exception cref="ArithmeticException"><paramref name="value" /> is less than 0.</exception>
+    public static long Factorial(this long value)
+    {
+        if (value < 0)
+        {
+            throw new ArithmeticException(nameof(value));
+        }
+
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1L;
+        for (var i = 1L; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}
diff --git a/X10D/src/Math/SByteExtensions.cs b/X10D/src/Math/SByteExtensions.cs
new file mode 100644
index 0000000..d9bc296
--- /dev/null
+++ b/X10D/src/Math/SByteExtensions.cs
@@ -0,0 +1,35 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="sbyte" />.
+/// </summary>
+[CLSCompliant(false)]
+public static class SByteExtensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 8-bit signed integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    /// <exception cref="ArithmeticException"><paramref name="value" /> is less than 0.</exception>
+    public static long Factorial(this sbyte value)
+    {
+        if (value < 0)
+        {
+            throw new ArithmeticException(nameof(value));
+        }
+
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1L;
+        for (ushort i = 1; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}
diff --git a/X10D/src/Math/UInt16Extensions.cs b/X10D/src/Math/UInt16Extensions.cs
new file mode 100644
index 0000000..bdbe702
--- /dev/null
+++ b/X10D/src/Math/UInt16Extensions.cs
@@ -0,0 +1,29 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="ushort" />.
+/// </summary>
+[CLSCompliant(false)]
+public static class UInt16Extensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 16-bit unsigned integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    public static ulong Factorial(this ushort value)
+    {
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1UL;
+        for (ushort i = 1; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}
diff --git a/X10D/src/Math/UInt32Extensions.cs b/X10D/src/Math/UInt32Extensions.cs
new file mode 100644
index 0000000..5f1aec0
--- /dev/null
+++ b/X10D/src/Math/UInt32Extensions.cs
@@ -0,0 +1,29 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="uint" />.
+/// </summary>
+[CLSCompliant(false)]
+public static class UInt32Extensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 32-bit unsigned integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    public static ulong Factorial(this uint value)
+    {
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1UL;
+        for (var i = 1U; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}
diff --git a/X10D/src/Math/UInt64Extensions.cs b/X10D/src/Math/UInt64Extensions.cs
new file mode 100644
index 0000000..3be7e06
--- /dev/null
+++ b/X10D/src/Math/UInt64Extensions.cs
@@ -0,0 +1,29 @@
+namespace X10D.Math;
+
+/// <summary>
+///     Extension methods for <see cref="ulong" />.
+/// </summary>
+[CLSCompliant(false)]
+public static class UInt64Extensions
+{
+    /// <summary>
+    ///     Returns the factorial of the current 64-bit unsigned integer.
+    /// </summary>
+    /// <param name="value">The value whose factorial to compute.</param>
+    /// <returns>The factorial of <paramref name="value" />.</returns>
+    public static ulong Factorial(this ulong value)
+    {
+        if (value == 0)
+        {
+            return 1;
+        }
+
+        var result = 1UL;
+        for (var i = 1UL; i <= value; i++)
+        {
+            result *= i;
+        }
+
+        return result;
+    }
+}