Calendar systems

Gregorian grid, second calendar underneath

In this release every calendar uses a Gregorian month grid (1900–2100). When you choose a second calendar, its date is printed under each Gregorian day. The months you select (for example February–April) are Gregorian months; a single Gregorian month can span two months — or even two years — of the second calendar, and the labels show that.

We do not yet offer calendars whose main grid follows another calendar's months. That is a separate product and will be labelled clearly if it is added.

How dates are calculated

Dates are computed by a stated method, never guessed by AI. The method in use is named on every preview under "Second-calendar method".

• Chinese lunar dates come from the Hong Kong Observatory's official 2027 Gregorian–lunar conversion table (HKO 2027 table, PDF). We use the table's month boundaries for every 2027 day, because a calculated (ICU) conversion disagrees with the official table on some 2027 dates. Unicode CLDR / ICU is used only for the wording: localized month and year names and numerals.
• Vietnamese lunar dates use a separate UTC+7 calculation (Hồ Ngọc Đức method), with leap-month labels. This is a calculation, not an official holiday determination.
• Other second calendars are converted with the Unicode CLDR / ICU calendar definitions built into the runtime (Intl), anchored to the Gregorian civil date.

| Calendar | Notes | | --- | --- | | Chinese lunar | Hong Kong Observatory 2027 table (no leap month falls in 2027). Traditional festivals are not shown, and lunar dates are not public holidays. | | Vietnamese lunar | Vietnam civil dates at UTC+7; distinct from the Chinese calendar. | | Japanese era | Era name and year (e.g. Reiwa 9 = 2027). | | Hijri (Umm al-Qura) | The Saudi Umm al-Qura tabulation. Actual dates in your country can differ by a day because of local moon sighting. | | Hijri (tabular) | An arithmetic calendar; it can differ from observed dates. | | Hebrew | Hebrew dates change at sunset; we show the date for the daytime of each Gregorian day. | | Persian (Solar Hijri) | The official calendar of Iran and Afghanistan. | | Thai Buddhist | Buddhist Era year (2027 = BE 2570). | | Minguo (ROC) | Year count used in Taiwan (2027 = Minguo 116). | | Indian national (Saka) | The Indian national civil calendar. |

Holidays

Calendar conversion, traditional festivals, public holidays and substitute workdays are different things. Regional presets can add a versioned 2027 holiday list from published sources: Singapore, Taiwan, Hong Kong, Indonesia, Vietnam, the Philippines, Kuala Lumpur and Thai financial institutions. Coverage and source links are shown before export. Philippine dates are incomplete pending separate declarations; the Kuala Lumpur list omits substitute days and is labelled partial. Indonesian collective leave and Philippine working observances have separate labels. Public-sector, bank and city scopes are explicit. Changing to a year without a verified list removes its holiday dates. Lunar calculations never create legal holidays. Custom date positions retain date marks and offer the holiday list as a separate CSV.

AI full images

When AI draws the whole calendar, it receives the same settings but may still draw wrong dates. Those images are always labelled "AI-drawn dates — not verified".