diff --git a/X10D.Tests/src/Time/DateTimeOffsetTests.cs b/X10D.Tests/src/Time/DateTimeOffsetTests.cs
new file mode 100644
index 0000000..ccd9206
--- /dev/null
+++ b/X10D.Tests/src/Time/DateTimeOffsetTests.cs
@@ -0,0 +1,69 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Time;
+
+namespace X10D.Tests.Time;
+
+[TestClass]
+public class DateTimeOffsetTests
+{
+    [TestMethod]
+    public void AgeShouldBeCorrect()
+    {
+        DateTimeOffset birthday = new DateTime(2000, 1, 1);
+        DateTimeOffset today = DateTime.Now.Date;
+
+        Assert.AreEqual(today.Year - birthday.Year, birthday.Age());
+    }
+
+    [TestMethod]
+    public void FirstShouldBeCorrect()
+    {
+        DateTimeOffset date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(2000, 1, 1), date.First(DayOfWeek.Saturday));
+        Assert.AreEqual(new DateTime(2000, 1, 2), date.First(DayOfWeek.Sunday));
+        Assert.AreEqual(new DateTime(2000, 1, 3), date.First(DayOfWeek.Monday));
+        Assert.AreEqual(new DateTime(2000, 1, 4), date.First(DayOfWeek.Tuesday));
+        Assert.AreEqual(new DateTime(2000, 1, 5), date.First(DayOfWeek.Wednesday));
+        Assert.AreEqual(new DateTime(2000, 1, 6), date.First(DayOfWeek.Thursday));
+        Assert.AreEqual(new DateTime(2000, 1, 7), date.First(DayOfWeek.Friday));
+    }
+
+    [TestMethod]
+    public void FirstDayOfMonthShouldBeCorrect()
+    {
+        DateTimeOffset today = DateTime.Now.Date;
+
+        Assert.AreEqual(new DateTime(today.Year, today.Month, 1), today.FirstDayOfMonth());
+    }
+
+    [TestMethod]
+    public void LastShouldBeCorrect()
+    {
+        DateTimeOffset date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(2000, 1, 29), date.Last(DayOfWeek.Saturday));
+        Assert.AreEqual(new DateTime(2000, 1, 30), date.Last(DayOfWeek.Sunday));
+        Assert.AreEqual(new DateTime(2000, 1, 31), date.Last(DayOfWeek.Monday));
+        Assert.AreEqual(new DateTime(2000, 1, 25), date.Last(DayOfWeek.Tuesday));
+        Assert.AreEqual(new DateTime(2000, 1, 26), date.Last(DayOfWeek.Wednesday));
+        Assert.AreEqual(new DateTime(2000, 1, 27), date.Last(DayOfWeek.Thursday));
+        Assert.AreEqual(new DateTime(2000, 1, 28), date.Last(DayOfWeek.Friday));
+    }
+
+    [TestMethod]
+    public void LastDayOfMonthShouldBeCorrect()
+    {
+        DateTimeOffset date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(date.Year, date.Month, 31), date.LastDayOfMonth());
+    }
+
+    [TestMethod]
+    public void NextShouldBeCorrect()
+    {
+        DateTimeOffset date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(2000, 1, 8), date.Next(DayOfWeek.Saturday));
+    }
+}
diff --git a/X10D.Tests/src/Time/DateTimeTests.cs b/X10D.Tests/src/Time/DateTimeTests.cs
new file mode 100644
index 0000000..f2e6aac
--- /dev/null
+++ b/X10D.Tests/src/Time/DateTimeTests.cs
@@ -0,0 +1,85 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using X10D.Time;
+
+namespace X10D.Tests.Time;
+
+[TestClass]
+public class DateTimeTests
+{
+    [TestMethod]
+    public void AgeShouldBeCorrect()
+    {
+        var birthday = new DateTime(2000, 1, 1);
+        DateTime today = DateTime.Now.Date;
+
+        Assert.AreEqual(today.Year - birthday.Year, birthday.Age());
+    }
+
+    [TestMethod]
+    public void FirstShouldBeCorrect()
+    {
+        var date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(2000, 1, 1), date.First(DayOfWeek.Saturday));
+        Assert.AreEqual(new DateTime(2000, 1, 2), date.First(DayOfWeek.Sunday));
+        Assert.AreEqual(new DateTime(2000, 1, 3), date.First(DayOfWeek.Monday));
+        Assert.AreEqual(new DateTime(2000, 1, 4), date.First(DayOfWeek.Tuesday));
+        Assert.AreEqual(new DateTime(2000, 1, 5), date.First(DayOfWeek.Wednesday));
+        Assert.AreEqual(new DateTime(2000, 1, 6), date.First(DayOfWeek.Thursday));
+        Assert.AreEqual(new DateTime(2000, 1, 7), date.First(DayOfWeek.Friday));
+    }
+
+    [TestMethod]
+    public void FirstDayOfMonthShouldBeCorrect()
+    {
+        DateTime today = DateTime.Now.Date;
+
+        Assert.AreEqual(new DateTime(today.Year, today.Month, 1), today.FirstDayOfMonth());
+    }
+
+    [TestMethod]
+    public void LastShouldBeCorrect()
+    {
+        var date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(2000, 1, 29), date.Last(DayOfWeek.Saturday));
+        Assert.AreEqual(new DateTime(2000, 1, 30), date.Last(DayOfWeek.Sunday));
+        Assert.AreEqual(new DateTime(2000, 1, 31), date.Last(DayOfWeek.Monday));
+        Assert.AreEqual(new DateTime(2000, 1, 25), date.Last(DayOfWeek.Tuesday));
+        Assert.AreEqual(new DateTime(2000, 1, 26), date.Last(DayOfWeek.Wednesday));
+        Assert.AreEqual(new DateTime(2000, 1, 27), date.Last(DayOfWeek.Thursday));
+        Assert.AreEqual(new DateTime(2000, 1, 28), date.Last(DayOfWeek.Friday));
+    }
+
+    [TestMethod]
+    public void LastDayOfMonthShouldBeCorrect()
+    {
+        var date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(date.Year, date.Month, 31), date.LastDayOfMonth());
+    }
+
+    [TestMethod]
+    public void NextShouldBeCorrect()
+    {
+        var date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(new DateTime(2000, 1, 8), date.Next(DayOfWeek.Saturday));
+    }
+
+    [TestMethod]
+    public void ToUnixTimeMillisecondsShouldBeCorrect()
+    {
+        var date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(946684800000, date.ToUnixTimeMilliseconds());
+    }
+
+    [TestMethod]
+    public void ToUnixTimeSecondsShouldBeCorrect()
+    {
+        var date = new DateTime(2000, 1, 1);
+
+        Assert.AreEqual(946684800, date.ToUnixTimeSeconds());
+    }
+}
diff --git a/X10D/src/DateTimeExtensions/DateTimeExtensions.cs b/X10D/src/Time/DateTimeExtensions.cs
similarity index 99%
rename from X10D/src/DateTimeExtensions/DateTimeExtensions.cs
rename to X10D/src/Time/DateTimeExtensions.cs
index b57550b..0d99a4f 100644
--- a/X10D/src/DateTimeExtensions/DateTimeExtensions.cs
+++ b/X10D/src/Time/DateTimeExtensions.cs
@@ -1,4 +1,4 @@
-namespace X10D;
+namespace X10D.Time;
 
 /// <summary>
 ///     Extension methods for <see cref="DateTime" />.
diff --git a/X10D/src/DateTimeExtensions/DateTimeOffsetExtensions.cs b/X10D/src/Time/DateTimeOffsetExtensions.cs
similarity index 99%
rename from X10D/src/DateTimeExtensions/DateTimeOffsetExtensions.cs
rename to X10D/src/Time/DateTimeOffsetExtensions.cs
index b7961fa..97df8f7 100644
--- a/X10D/src/DateTimeExtensions/DateTimeOffsetExtensions.cs
+++ b/X10D/src/Time/DateTimeOffsetExtensions.cs
@@ -1,4 +1,4 @@
-namespace X10D;
+namespace X10D.Time;
 
 /// <summary>
 ///     Extension methods for <see cref="DateTimeOffset" />.