diff --git a/src/main.zig b/src/main.zig
index ba688c6..e524042 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -3,154 +3,14 @@ const debug = std.debug;
 const testing = std.testing;
 pub const Year = @import("year.zig").Year;
 pub const Month = @import("month.zig").Month;
+pub const tz = @import("timezone.zig");
+pub const Offset = tz.Offset;
+pub const TimeZone = tz.TimeZone;
 
 pub const SECONDS_PER_MINUTE = 60;
 pub const SECONDS_PER_HOUR = 60 * 60;
 pub const SECONDS_PER_DAY = SECONDS_PER_HOUR * 24;
 
-pub const TimeZoneTag = enum(u1) {
-    utc,
-    offset,
-};
-
-pub const Sign = enum(u1) {
-    positive,
-    negative,
-};
-
-const HoursMinutes = struct {
-    hours: u4,
-    minutes: ?u6,
-};
-
-pub const Offset = union(Sign) {
-    positive: HoursMinutes,
-    negative: HoursMinutes,
-
-    const Self = @This();
-
-    fn new(hours: i8, minutes: ?u6) ?Self {
-        if (hours > 12 or hours < -12) {
-            return null;
-        }
-        if (minutes) |m| {
-            if (m > 59) return null;
-            if (hours == 0 and m == 0) return null;
-        } else if (hours == 0) return null;
-        if (hours < 0) {
-            const h = @intCast(u4, @as(i8, hours) * -1);
-            return Self{ .negative = .{ .hours = h, .minutes = minutes } };
-        } else {
-            return Self{ .positive = .{ .hours = @intCast(u4, hours), .minutes = minutes } };
-        }
-    }
-
-    fn asSeconds(self: Self) i64 {
-        return switch (self) {
-            .positive => |ofs| blk: {
-                var seconds = @as(i64, ofs.hours) * 3600;
-                if (ofs.minutes) |m| seconds += (@as(i64, m) * 60);
-                break :blk seconds;
-            },
-            .negative => |ofs| blk: {
-                var seconds = @as(i64, ofs.hours) * 3600;
-                if (ofs.minutes) |m| seconds += (@as(i64, m) * 60);
-                break :blk seconds * -1;
-            },
-        };
-    }
-};
-
-test "new year" {
-    try testing.expectEqual(Year.new(2023), Year{ .normal = 2023 });
-    try testing.expectEqual(Year.new(2024), Year{ .leap = 2024 });
-    debug.print("Passed\n", .{});
-}
-
-test "get year" {
-    try testing.expectEqual(Year.new(2023).get(), 2023);
-    try testing.expectEqual(Year.new(2024).get(), 2024);
-    debug.print("Passed\n", .{});
-}
-
-test "next year" {
-    try testing.expectEqual(Year.new(2023).next(), Year{ .leap = 2024 });
-    debug.print("Passed\n", .{});
-}
-
-test "last year" {
-    try testing.expectEqual(Year.new(2024).previous(), Year{ .normal = 2023 });
-    debug.print("Passed\n", .{});
-}
-
-test "get days in month" {
-    const year = Year.new(2023);
-    const month = Month.february;
-    try testing.expectEqual(month.days(year), 28);
-    debug.print("Passed\n", .{});
-}
-
-test "next month" {
-    try testing.expectEqual(Month.june.next(), .july);
-    try testing.expectEqual(Month.december.next(), null);
-    debug.print("Passed\n", .{});
-}
-
-test "last month" {
-    try testing.expectEqual(Month.june.previous(), .may);
-    try testing.expectEqual(Month.january.previous(), null);
-    debug.print("Passed\n", .{});
-}
-
-test "new offsets" {
-    try testing.expectEqual(Offset.new(-5, null), Offset{ .negative = .{ .hours = 5, .minutes = null } });
-    try testing.expectEqual(Offset.new(3, null), Offset{ .positive = .{ .hours = 3, .minutes = null } });
-    debug.print("Passed\n", .{});
-}
-
-test "as seconds" {
-    try testing.expectEqual(Offset.new(-4, 30).?.asSeconds(), -16200);
-    try testing.expectEqual(Offset.new(3, null).?.asSeconds(), 10800);
-    debug.print("Passed\n", .{});
-}
-
-pub const TimeZone = union(TimeZoneTag) {
-    utc: void,
-    offset: Offset,
-
-    const Self = @This();
-
-    pub fn new(hours: ?i8, minutes: ?u6) ?Self {
-        return if (hours) |h| blk: {
-            if (h == 0) {
-                break :blk .utc;
-            } else if (Offset.new(h, minutes)) |ofs| {
-                break :blk Self{ .offset = ofs };
-            } else {
-                break :blk null;
-            }
-        } else if (minutes) |m| Self{ .offset = Offset.new(0, m).? } else .utc;
-    }
-};
-
-test "new timezone" {
-    const tz = TimeZone.new(-5, null).?;
-    try testing.expectEqual(@as(TimeZoneTag, tz), .offset);
-    switch (tz) {
-        .offset => |ofs| try testing.expectEqual(ofs, Offset{ .negative = .{ .hours = 5, .minutes = null } }),
-        else => unreachable,
-    }
-    debug.print("Passed\n", .{});
-}
-
-test "new timezone utc" {
-    const tz0 = TimeZone.new(null, null).?;
-    const tz1 = TimeZone.new(0, null).?;
-    try testing.expectEqual(@as(TimeZoneTag, tz0), .utc);
-    try testing.expectEqual(@as(TimeZoneTag, tz1), .utc);
-    debug.print("Passed\n", .{});
-}
-
 pub const WeekDay = enum(u3) {
     thursday = 0,
     friday,
@@ -323,6 +183,77 @@ pub const DateTime = struct {
     }
 };
 
+test "new year" {
+    try testing.expectEqual(Year.new(2023), Year{ .normal = 2023 });
+    try testing.expectEqual(Year.new(2024), Year{ .leap = 2024 });
+    debug.print("Passed\n", .{});
+}
+
+test "get year" {
+    try testing.expectEqual(Year.new(2023).get(), 2023);
+    try testing.expectEqual(Year.new(2024).get(), 2024);
+    debug.print("Passed\n", .{});
+}
+
+test "next year" {
+    try testing.expectEqual(Year.new(2023).next(), Year{ .leap = 2024 });
+    debug.print("Passed\n", .{});
+}
+
+test "last year" {
+    try testing.expectEqual(Year.new(2024).previous(), Year{ .normal = 2023 });
+    debug.print("Passed\n", .{});
+}
+
+test "get days in month" {
+    const year = Year.new(2023);
+    const month = Month.february;
+    try testing.expectEqual(month.days(year), 28);
+    debug.print("Passed\n", .{});
+}
+
+test "next month" {
+    try testing.expectEqual(Month.june.next(), .july);
+    try testing.expectEqual(Month.december.next(), null);
+    debug.print("Passed\n", .{});
+}
+
+test "last month" {
+    try testing.expectEqual(Month.june.previous(), .may);
+    try testing.expectEqual(Month.january.previous(), null);
+    debug.print("Passed\n", .{});
+}
+
+test "new offsets" {
+    try testing.expectEqual(Offset.new(-5, null), Offset{ .negative = .{ .hours = 5, .minutes = null } });
+    try testing.expectEqual(Offset.new(3, null), Offset{ .positive = .{ .hours = 3, .minutes = null } });
+    debug.print("Passed\n", .{});
+}
+
+test "as seconds" {
+    try testing.expectEqual(Offset.new(-4, 30).?.asSeconds(), -16200);
+    try testing.expectEqual(Offset.new(3, null).?.asSeconds(), 10800);
+    debug.print("Passed\n", .{});
+}
+
+test "new timezone" {
+    const zone = TimeZone.new(-5, null).?;
+    try testing.expectEqual(@as(tz.TimeZoneTag, zone), .offset);
+    switch (zone) {
+        .offset => |ofs| try testing.expectEqual(ofs, Offset{ .negative = .{ .hours = 5, .minutes = null } }),
+        else => unreachable,
+    }
+    debug.print("Passed\n", .{});
+}
+
+test "new timezone utc" {
+    const tz0 = TimeZone.new(null, null).?;
+    const tz1 = TimeZone.new(0, null).?;
+    try testing.expectEqual(@as(tz.TimeZoneTag, tz0), .utc);
+    try testing.expectEqual(@as(tz.TimeZoneTag, tz1), .utc);
+    debug.print("Passed\n", .{});
+}
+
 test "get year" {
     const dt = DateTime{
         .year = Year.new(2023),
diff --git a/src/timezone.zig b/src/timezone.zig
new file mode 100644
index 0000000..939e47b
--- /dev/null
+++ b/src/timezone.zig
@@ -0,0 +1,75 @@
+const std = @import("std");
+const debug = std.debug;
+const testing = std.testing;
+
+pub const TimeZoneTag = enum(u1) {
+    utc,
+    offset,
+};
+
+pub const Sign = enum(u1) {
+    positive,
+    negative,
+};
+
+const HoursMinutes = struct {
+    hours: u4,
+    minutes: ?u6,
+};
+
+pub const Offset = union(Sign) {
+    positive: HoursMinutes,
+    negative: HoursMinutes,
+
+    const Self = @This();
+
+    pub fn new(hours: i8, minutes: ?u6) ?Self {
+        if (hours > 12 or hours < -12) {
+            return null;
+        }
+        if (minutes) |m| {
+            if (m > 59) return null;
+            if (hours == 0 and m == 0) return null;
+        } else if (hours == 0) return null;
+        if (hours < 0) {
+            const h = @intCast(u4, @as(i8, hours) * -1);
+            return Self{ .negative = .{ .hours = h, .minutes = minutes } };
+        } else {
+            return Self{ .positive = .{ .hours = @intCast(u4, hours), .minutes = minutes } };
+        }
+    }
+
+    pub fn asSeconds(self: Self) i64 {
+        return switch (self) {
+            .positive => |ofs| blk: {
+                var seconds = @as(i64, ofs.hours) * 3600;
+                if (ofs.minutes) |m| seconds += (@as(i64, m) * 60);
+                break :blk seconds;
+            },
+            .negative => |ofs| blk: {
+                var seconds = @as(i64, ofs.hours) * 3600;
+                if (ofs.minutes) |m| seconds += (@as(i64, m) * 60);
+                break :blk seconds * -1;
+            },
+        };
+    }
+};
+
+pub const TimeZone = union(TimeZoneTag) {
+    utc: void,
+    offset: Offset,
+
+    const Self = @This();
+
+    pub fn new(hours: ?i8, minutes: ?u6) ?Self {
+        return if (hours) |h| blk: {
+            if (h == 0) {
+                break :blk .utc;
+            } else if (Offset.new(h, minutes)) |ofs| {
+                break :blk Self{ .offset = ofs };
+            } else {
+                break :blk null;
+            }
+        } else if (minutes) |m| Self{ .offset = Offset.new(0, m).? } else .utc;
+    }
+};