diff --git a/CLAUDE.md b/CLAUDE.md
index 56d5bea..2f73baf 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -28,7 +28,8 @@ is the living showcase — new engine features are demonstrated there.
 Engine libraries (each feature is a namespaced subfolder of its host):
 
 - **`Core`** — game loop, ECS world, scenes, time (`GameClock` with `TimeScale`; `GameSpeed`
-  for discrete pause/1×/3×/6× speed control over the clock, `context.UseGameSpeed(...)`),
+  for discrete pause/1×/3×/6× speed control over the clock, `context.UseGameSpeed(...)`;
+  `Calendar` turning scaled time into in-game days, `context.UseCalendar(secondsPerDay)`),
   plus **Input** (`MrGameEng.Input`: `InputManager`, `ActionMap`, `InputSystem`, in
   `Core/Input/`). Depends only on MonoGame and Friflo.Engine.ECS.
 - **`Graphics`** — custom batched renderer, camera, sprites, plus **Tilemaps**
diff --git a/docs/architecture.md b/docs/architecture.md
index 7aec8d9..1f0328c 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -33,7 +33,7 @@
 
 | Библиотека (сборка)          | Фичи (неймспейсы) и ответственность                        |
 |------------------------------|------------------------------------------------------------|
-| `MrGameEng.Core`             | Игровой цикл (хост над `Game`), `EntityStore`, `SystemRoot`, сцены, время (`GameClock.TimeScale`; `GameSpeed` — дискретная скорость пауза/1×/3×/6× поверх часов), жизненный цикл. **Input** (`MrGameEng.Input`, `Core/Input/`): клавиатура, мышь, геймпад, action maps |
+| `MrGameEng.Core`             | Игровой цикл (хост над `Game`), `EntityStore`, `SystemRoot`, сцены, время (`GameClock.TimeScale`; `GameSpeed` — дискретная скорость пауза/1×/3×/6× поверх часов; `Calendar` — игровые дни поверх масштабированного времени, `context.UseCalendar(...)`), жизненный цикл. **Input** (`MrGameEng.Input`, `Core/Input/`): клавиатура, мышь, геймпад, action maps |
 | `MrGameEng.Graphics`         | Собственный батчер-рендерер (см. «Рендеринг»), камера, спрайты, анимации, слои. **Tilemaps** (`MrGameEng.Tilemaps`, `Graphics/Tilemaps/`): тайловые карты кодом — `TileGrid` + `TileSet` + компонент `Tilemap`, отрисовка видимых клеток через батчер |
 | `MrGameEng.Audio`            | Звуковые эффекты и музыка (NVorbis); `AudioManager` с `SoundVolume`/`MasterVolume` (одна ручка на эффекты и музыку) |
 | `MrGameEng.Content`          | Пайплайн контента. **Assets** (`MrGameEng.Assets`): runtime-загрузка без Content Pipeline, кэш, `AssetRef<T>`. **Atlases** (`MrGameEng.Atlases`): текстурные атласы — сборка из дерева картинок (`AtlasBuilder`) и рантайм-загрузка (`TextureAtlas`), CLI `tools/MrGameEng.AtlasTool`. **Mods** (`MrGameEng.Mods`): система модов — порядок загрузки, JSON-дефы, локализация, слияние деревьев контента |
diff --git a/src/MrGameEng.Core/Calendar.cs b/src/MrGameEng.Core/Calendar.cs
new file mode 100644
index 0000000..b64fca8
--- /dev/null
+++ b/src/MrGameEng.Core/Calendar.cs
@@ -0,0 +1,70 @@
+namespace MrGameEng.Core;
+
+/// <summary>
+/// In-game calendar layered over <see cref="GameClock"/>: turns scaled elapsed time into whole
+/// days and a fraction-of-day (time of day). One in-game day spans <see cref="SecondsPerDay"/>
+/// seconds of scaled clock time, so pausing or changing <see cref="GameClock.TimeScale"/> slows
+/// or stops the calendar automatically. Pure read-side, GPU-free and deterministic; registered as
+/// a service via <see cref="CalendarEngineExtensions.UseCalendar"/>.
+/// </summary>
+public sealed class Calendar
+{
+    private readonly GameClock _clock;
+    private float _secondsPerDay;
+
+    /// <summary>
+    /// Creates a calendar reading <paramref name="clock"/>; one day spans
+    /// <paramref name="secondsPerDay"/> seconds of scaled time (must be positive).
+    /// </summary>
+    public Calendar(GameClock clock, float secondsPerDay)
+    {
+        _clock = clock ?? throw new ArgumentNullException(nameof(clock));
+        SecondsPerDay = secondsPerDay;
+    }
+
+    /// <summary>Scaled seconds per in-game day. Must be positive; raising it slows the calendar.</summary>
+    public float SecondsPerDay
+    {
+        get => _secondsPerDay;
+        set =>
+            _secondsPerDay =
+                value > 0f
+                    ? value
+                    : throw new ArgumentOutOfRangeException(
+                        nameof(value),
+                        "Seconds per day must be positive."
+                    );
+    }
+
+    /// <summary>Total elapsed days as a continuous value (e.g. 3.5 = midday of day 4).</summary>
+    public double TotalDays => _clock.TotalTime / _secondsPerDay;
+
+    /// <summary>The current day number, counting from 1.</summary>
+    public int Day => (int)TotalDays + 1;
+
+    /// <summary>Progress through the current day in <c>[0, 1)</c> — 0 at dawn, ~0.5 at midday.</summary>
+    public float DayProgress
+    {
+        get
+        {
+            var days = TotalDays;
+            return (float)(days - Math.Floor(days));
+        }
+    }
+}
+
+/// <summary>Wires the in-game calendar into the engine.</summary>
+public static class CalendarEngineExtensions
+{
+    /// <summary>
+    /// Creates a <see cref="Calendar"/> bound to the context's clock and registers it as a
+    /// service. Call once per world. <paramref name="secondsPerDay"/> is the scaled-time length
+    /// of one in-game day (must be positive).
+    /// </summary>
+    public static Calendar UseCalendar(this EngineContext context, float secondsPerDay)
+    {
+        var calendar = new Calendar(context.Clock, secondsPerDay);
+        context.Services.Add(calendar);
+        return calendar;
+    }
+}
diff --git a/tests/MrGameEng.Core.Tests/CalendarTests.cs b/tests/MrGameEng.Core.Tests/CalendarTests.cs
new file mode 100644
index 0000000..43fcbb2
--- /dev/null
+++ b/tests/MrGameEng.Core.Tests/CalendarTests.cs
@@ -0,0 +1,69 @@
+using MrGameEng.Core;
+using Xunit;
+
+namespace MrGameEng.Core.Tests;
+
+public class CalendarTests
+{
+    [Fact]
+    public void Constructor_NonPositiveSecondsPerDay_Throws()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() => new Calendar(new GameClock(), 0f));
+    }
+
+    [Fact]
+    public void TotalDays_TracksScaledClockTime()
+    {
+        var clock = new GameClock();
+        var calendar = new Calendar(clock, secondsPerDay: 10f);
+
+        clock.Advance(5f); // half a day
+
+        Assert.Equal(0.5, calendar.TotalDays, 5);
+        Assert.Equal(1, calendar.Day);
+        Assert.Equal(0.5f, calendar.DayProgress, 5);
+    }
+
+    [Fact]
+    public void Day_CountsFromOne_AndRollsOver()
+    {
+        var clock = new GameClock();
+        var calendar = new Calendar(clock, secondsPerDay: 10f);
+
+        Assert.Equal(1, calendar.Day);
+
+        clock.Advance(10f); // exactly one day
+        Assert.Equal(2, calendar.Day);
+        Assert.Equal(0f, calendar.DayProgress, 5);
+
+        clock.Advance(15f); // total 25s = 2.5 days
+        Assert.Equal(3, calendar.Day);
+        Assert.Equal(0.5f, calendar.DayProgress, 5);
+    }
+
+    [Fact]
+    public void Pause_DoesNotAdvanceTheCalendar()
+    {
+        var clock = new GameClock { TimeScale = 0f };
+        var calendar = new Calendar(clock, secondsPerDay: 10f);
+
+        clock.Advance(100f);
+
+        Assert.Equal(0.0, calendar.TotalDays, 5);
+        Assert.Equal(1, calendar.Day);
+    }
+
+    [Fact]
+    public void TimeScale_SpeedsUpTheCalendar()
+    {
+        var slow = new GameClock();
+        var fast = new GameClock { TimeScale = 6f };
+        var slowCal = new Calendar(slow, secondsPerDay: 10f);
+        var fastCal = new Calendar(fast, secondsPerDay: 10f);
+
+        slow.Advance(10f);
+        fast.Advance(10f);
+
+        Assert.Equal(6.0, fastCal.TotalDays / slowCal.TotalDays, 5);
+    }
+}