Myanmar Calendar for Kotlin Multiplatform

A pure Kotlin Myanmar calendar library and interactive Kotlin Multiplatform demo. It runs from shared code on Android and iOS and converts dates in both directions:

• Gregorian (English) date → Myanmar date
• Myanmar date → Gregorian (English) date
• Gregorian/Myanmar date strings with custom numeric patterns
• Moon phase, fortnight day, Sabbath status, weekday, and localized display names
• Gregorian-month and Myanmar lunar-month calendar views
• Recurring Myanmar calendar observances for past and future years, plus verified annual official-holiday data where available
• Pluggable holiday rules and a compact sample API for app integration

The calendar engine has no Android, iOS, or Compose dependency. The Compose UI is only a demo consumer of the shared library.

shared/src/commonMain/kotlin/com/aj/mmp_multi/myanmarcalendar/
├── calendar_core/
│   ├── model/       # Public data types and enums
│   ├── engine/      # Myanmar calendar algorithm (internal)
│   ├── converter/   # Gregorian ↔ Julian-day conversion helpers
│   ├── util/        # Gregorian validation and leap-year helpers
│   ├── internal/    # Algorithm constants (internal)
│   └── MyanmarCalendar.kt
├── calendar_formatter/  # Numeric parsing and Myanmar/English formatting
├── calendar_holiday/    # Pluggable holiday-rule API
├── calendar_astrology/  # Calendar weekday helper
└── sample/              # Minimal non-UI sample

commonMain.dependencies {
    implementation("io.github.newarjun101:mmcalendar:$latestVersion")
}

Define latestVersion yourself in your version catalog, build constants, or Gradle configuration.

Ensure your project includes Maven Central:

repositories {
    mavenCentral()
}

After adding the dependency, use the library from commonMain, androidMain, or iosMain.

import com.newarjun101.mmcalendar.calendar_core.MyanmarCalendar
import com.newarjun101.mmcalendar.calendar_core.model.GregorianDate
import com.newarjun101.mmcalendar.calendar_formatter.MyanmarDateFormatter

val gregorian = GregorianDate(2024, 4, 17)
val myanmar = MyanmarCalendar.fromGregorian(gregorian)

println(myanmar.year) // 1386
println(MyanmarDateFormatter.format(myanmar))
// တန်ခူး လဆန်း ၉

Visit the demo project to see MMCalendar in action:

https://github.com/newarjun101/myanmar-calendar-demo

val myanmar = MyanmarCalendar.fromGregorian(2024, 4, 17)

// Or use a validated value object.
val myanmar2 = MyanmarCalendar.fromGregorian(GregorianDate(2024, 4, 17))

GregorianDate validates the month and day, including Gregorian leap years. Invalid values throw IllegalArgumentException.

val english = MyanmarCalendar.toGregorian(myanmar)

// Or provide Myanmar year, month, and day directly.
val english2 = MyanmarCalendar.toGregorian(
    year = 1386,
    month = 1,
    day = 9,
)

Myanmar input is validated against the calendar engine. For example, First Waso (month = 0) is accepted only in a watat year.

val jdn = MyanmarCalendar.toJulianDayNumber(GregorianDate(2000, 1, 1))
// 2451545

val myanmar = MyanmarCalendar.fromJulianDayNumber(jdn)
val jdnFromMyanmar = MyanmarCalendar.toJulianDayNumber(
    year = myanmar.year,
    month = myanmar.month,
    day = myanmar.day,
)

MyanmarCalendar.fromGregorian(...) returns MyanmarDate:

Myanmar calendar years can contain an intercalary month (watat) to keep lunar months aligned with the solar year.

First Waso is represented by month = 0; it is valid only in a watat year. The yearType is calculated by the engine, so callers normally read it from MyanmarDate instead of setting it themselves.

The engine assigns a phase from the Myanmar calendar day:

For display, prefer MyanmarDateFormatter.moonPhaseName(date.moonPhase) and MyanmarDateFormatter.format(date). This correctly renders labels such as လဆန်း, လပြည့်, လဆုတ်, and လကွယ်.

sabbathDay is a Myanmar lunar observance marker, not a public-holiday decision:

Use sabbathDay to decorate a calendar UI or to apply app-specific observance logic. Use MyanmarHolidayCalendar for actual holiday policy.

Use MyanmarDateFormatter.monthName(...) rather than hard-coding names in UI.

Gregorian formatting supports yyyy, yy, MM, M, dd, and d.

import com.newarjun101.mmcalendar.calendar_formatter.GregorianDateFormatter

val text = GregorianDateFormatter.format(
    GregorianDate(2024, 4, 17),
    pattern = "dd.MM.yyyy",
)
// 17.04.2024

Myanmar formatting supports all of the above plus MMMM for the localized month name.

import com.newarjun101.mmcalendar.calendar_core.model.MyanmarLanguage
import com.newarjun101.mmcalendar.calendar_formatter.MyanmarDateFormatter

val myanmarText = MyanmarDateFormatter.format(myanmar, "yyyy MMMM dd")
// ၁၃၈၆ တန်ခူး ၀၉

val englishText = MyanmarDateFormatter.format(
    myanmar,
    pattern = "yyyy MMMM dd",
    language = MyanmarLanguage.ENGLISH,
)
// 1386 Tagu 09

CalendarDateConverter accepts numeric date strings. Input patterns require each of these tokens exactly once:

• yyyy — year
• MM or M — month
• dd or d — day

All non-token characters are treated as literal separators, so -, /, ., and spaces can be used. Myanmar input accepts either Myanmar digits (၁၃၈၆) or Western digits (1386). Month names (MMMM) and two-digit years (yy) are output-only.

import com.newarjun101.mmcalendar.calendar_formatter.CalendarDateConverter

val myanmarText = CalendarDateConverter.gregorianToMyanmar(
    text = "17/04/2024",
    inputPattern = "dd/MM/yyyy",
    outputPattern = "yyyy MMMM dd",
)

val gregorianText = CalendarDateConverter.myanmarToGregorian(
    text = "၁၃၈၆-၁-၉",
    inputPattern = "yyyy-M-d",
    outputPattern = "dd.MM.yyyy",
)
// 17.04.2024

For a typed result instead of a string, use parseGregorian(...) or parseMyanmar(...).

val month = MyanmarDateFormatter.monthName(myanmar.month)
val phase = MyanmarDateFormatter.moonPhaseName(myanmar.moonPhase)
val digits = MyanmarDateFormatter.number(myanmar.year)

By default, formatter methods return Myanmar text and Myanmar digits. Pass MyanmarLanguage.ENGLISH when English names and Western digits are required.

import com.newarjun101.mmcalendar.calendar_astrology.MyanmarAstrology

val weekday = MyanmarAstrology.weekday(GregorianDate(2024, 4, 17))
// Weekday.WEDNESDAY

calendar_astrology currently exposes calendar weekday data only. Traditional astrological rules can be built on top of this stable input.

Holiday policy differs by locale and official observance, so the library deliberately does not hard-code a national holiday list. Supply rules from your app:

import com.newarjun101.mmcalendar.calendar_holiday.CalendarHoliday
import com.newarjun101.mmcalendar.calendar_holiday.HolidayRule
import com.newarjun101.mmcalendar.calendar_holiday.MyanmarHolidayCalendar

val holidays = MyanmarHolidayCalendar(
    HolidayRule { year ->
        listOf(CalendarHoliday("new-year", "New Year", GregorianDate(year, 1, 1)))
    },
)

val holidaysIn2024 = holidays.holidaysFor(2024)

MyanmarPublicHolidays.holidaysFor(2026) provides the published 2026 public-holiday list, including multi-day festivals. MyanmarHolidayCatalog.holidaysFor(year) is the demo-friendly option: it generates recurring calendar observances for any past or future year and merges any verified annual official list. Each CalendarHoliday has a kind of OFFICIAL or CALENDAR_OBSERVANCE so the UI can show the distinction.

The demo in shared/src/commonMain/kotlin/com/aj/mmp_multi/App.kt is fully stateful and demonstrates the public API.

Month colors: red ● full moon, blue ○ new moon, green ✦ Sabbath.

Build the Android demo:

./gradlew :androidApp:assembleDebug

For iOS, open iosApp in Xcode and run the iosApp scheme.

• The engine uses pure Kotlin and has no platform date/time dependency.
• Date-string parsing is intentionally numeric and strict; use typed APIs for business/domain code whenever possible.
• Official holiday observance and traditional astrology rules are app-specific extension points, not built-in assertions by this library.
• This repository contains the library source in its shared module; publishing it as an independent Maven artifact is a separate build/release step.

The Myanmar calendar conversion logic in calendar_core is a Kotlin Multiplatform port/adaptation of the calendrical algorithms from yan9a/mmcal, a Myanmar calendar implementation maintained by Yan Naing Aye and its contributors. The upstream project provides C++ and JavaScript implementations of modern Myanmar calendrical calculations under the MIT License.

Special thanks to the contributors who made the underlying algorithms and reference implementation available to the community:

• Ko Yan Naing Aye
• Mr Ko Ko Ye
• Ko Han Thu Htun
• Ko Chan Mrate Ko Ko

Thank you to these contributors and all contributors to yan9a/mmcal.

This project’s Kotlin API design, Kotlin Multiplatform demo, format utilities, holiday catalog, and documentation are maintained in this repository.

Copyright (c) 2026 Arjun Dhakal

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.