Hijri date converter

What this converter is doing

It counts days. Both calendars are turned into a single running day number, the conversion happens there, and the result is turned back into a date. That is why the weekday is always right even when the Hijri date is arguable, the day of the week belongs to the Gregorian date you entered, and only the Islamic date depends on which calendar you are reckoning by.

The part that is genuinely uncertain

The Islamic calendar in daily use begins each month when the new crescent is sighted. That is an observation, announced locally, and it cannot be known in advance. What a converter does instead is apply a fixed arithmetic scheme: twelve months alternating between 30 and 29 days, with eleven leap years in every thirty-year cycle.

The two drift against each other. A calculated date is usually within a day of the announced one, sometimes two, and can fall on either side. Two countries can be a day apart from each other on the same date. None of that is a fault in the arithmetic; it is what happens when a fixed scheme approximates an observation.

Three calendars, three answers

There is no single calculated Islamic calendar. The civil tabular variant and the astronomical tabular variant differ only in where they place the epoch, which puts them exactly one day apart forever. Saudi Arabia’s Umm al-Qura calendar is a third scheme, published as a table rather than computed from a formula, and it agrees with neither reliably. This tool shows you both tabular answers at once so the disagreement is a number rather than a footnote.

Making it match the calendar you actually use

If your mosque or country is a day ahead of what this gives, the shift control moves every date the tool produces. It is the honest way to use a converter: take the announced date as correct and adjust the arithmetic to agree with it, rather than the other way round.

When a converted date is good enough

For working out roughly when something falls, for filling in a form, for planning several months out, or for converting a date of birth recorded in one calendar into the other, a tabular conversion is fine and is what most official systems use. For deciding when to start fasting or when Eid is, it is not, those come from an announcement, and no calculator can stand in for one.