Tabular Day of Ashura date calculator

It uses the fixed arithmetic Islamic calendar, so the same input always produces the same output in every environment. The response includes the Gregorian date, weekday, calendar labels, and UTC basis. It is intended for software, reproducible research, teaching, and datasets that explicitly use the tabular model, not for declaring a locally observed or officially announced religious date.

Understand exactly which Ashura date is calculated

Ashura falls on the tenth day of Muharram, but converting that Hijri date to a civil date requires choosing an Islamic calendar model. This calculator uses the tabular Islamic calendar, also called the arithmetic or civil Islamic calendar in some technical references. That model assigns month lengths and leap years through a fixed repeating rule. Enter a positive whole-number Hijri year, such as 1446, and the result maps 10 Muharram of that year to the proleptic Gregorian calendar. The output states both calendar models so a stored result remains understandable outside the original request. It also reports UTC because the calculation represents a calendar day deterministically, without consulting a device timezone. This distinction matters: communities may begin a Hijri month from local crescent sighting, an official announcement, an astronomical visibility criterion, or a published national calendar. Those approaches can place 10 Muharram on a different Gregorian day. Use this endpoint only when a tabular result is the intended answer, and do not present it as a religious ruling or local announcement.

How the deterministic conversion works

The calculation first determines the integer Julian day number for 10 Muharram in the requested tabular Hijri year. It starts from the fixed civil Islamic epoch, adds the complete years before the input year, and applies the tabular calendar's thirty-year leap-cycle term. Because Muharram is the first month, there are no preceding months to sum for this particular observance. The resulting day number is then converted with integer arithmetic into a year, month, and day in the proleptic Gregorian calendar. The weekday is derived from that same day number, keeping every returned field internally consistent. No JavaScript Date object is constructed, so host timezone settings, daylight-saving rules, locale parsing, and differences in date-library support cannot alter the answer. The solver also does not read the current time or make a network request. Input validation requires a numeric, positive, safe integer. Numeric strings, decimals, zero, negative years, infinity, and values whose intermediate day number cannot remain exact are rejected instead of being silently coerced into a plausible-looking date.

Use the result safely in applications and datasets

This capability is useful when reproducibility is more important than reconstructing a historical sighting or predicting a future official declaration. A developer can generate stable fixtures for calendar software, normalize records whose source explicitly says arithmetic Islamic calendar, prepare a teaching timeline, or compare independent implementations of the same rule. Store the returned Hijri year, Gregorian date, and calendar labels together; retaining only the Gregorian date can hide the assumption that produced it. If your source uses Umm al-Qura, a national ministry calendar, astronomical crescent visibility, or local observation, compare against a service designed for that source instead. Near a month boundary, a one-day difference does not necessarily mean either system has a programming error; it may reflect different calendar definitions. The API charge is $0.002 per request. Since the function is pure and each year has one stable tabular answer, applications may cache results by Hijri year. UTC in the output signals the deterministic mapping basis, not an assertion that every community begins the religious day at the same instant.