Data Sources

Developer TODO: replace bracketed placeholders below with real business details before launch.

This page explains how Tomorrow Calendar's calendar, holiday, festival and timezone information is put together.

Date & calendar calculations

All date arithmetic — tomorrow's date, week numbers, day-of-year counts, calendar grids and the results in our date tools — is calculated algorithmically using the proleptic Gregorian calendar and your browser's IANA timezone database. Nothing here is hard-coded; every date is computed live.

Holiday & festival data

Fixed-date national/federal/statutory holidays (for example New Year's Day or a country's independence day) are listed with high confidence. Holidays and festivals that depend on lunar or lunisolar observation (for example Eid, Chinese New Year, or certain Hindu festivals) are marked estimated where their exact Gregorian date is not yet officially confirmed, and are updated once official confirmation is available.

We do not invent or guess at holiday or festival dates. Where we are not confident in a date, we omit it rather than publish a guess.

Timezone data

Timezone handling uses the IANA Time Zone Database via your browser's built-in Intl API, which correctly accounts for daylight saving transitions.

Developer TODO: as the site grows, name specific upstream holiday-data providers or government sources here if/when a structured data feed is adopted.

Last updated: September 9, 2026.