Here is exactly how the tools work, so you know where each result comes from and can check it yourself.
Hijri calendar source
We use the Umm al-Qura calendar, the official Hijri calendar of Saudi Arabia. Month lengths (29 or 30 days) for 1300-1500 AH come from the Umm al-Qura table built into the ICU library used by browsers and operating systems. We ship that table with the site so results are identical on every device.
- Supported range: 1 Muharram 1300 AH (12 November 1882) to 30 Dhu al-Hijjah 1500 AH (16 November 2077).
- Every day in that range (over 71,000 days) is tested automatically in both directions.
Age and duration algorithm
- Both dates are converted to an absolute day number, so the number of days between them is exact regardless of calendar.
- To express the span in years, months and days we subtract the two dates in the chosen calendar: days from days, months from months, years from years.
- If the days are negative we borrow a month and add the length of the month before the end date (its real Umm al-Qura or Gregorian length); if the months are negative we borrow a year and add 12 months.
- If the start day is larger than that month (31 January → 1 March), the start day is clamped to the month's end, so the result is 1 month and 1 day, never negative days.
This is the method used by hand and by most calculators. Some sites differ by one day in Hijri age because they assume 30-day months or borrow from a different month.
Birthdays
The next birthday is the first anniversary on or after today. People born on 29 February celebrate on 28 February in non-leap years; people born on the 30th of a Hijri month celebrate on the 29th when that month has 29 days.
Ramadan and Eid dates
The start of Ramadan, Eid al-Fitr (1 Shawwal) and Eid al-Adha (10 Dhu al-Hijjah) come from the Umm al-Qura table; countdowns run to midnight Makkah time (UTC+3). Official dates are announced after the moon sighting and may differ by a day.
Test cases you can verify
| Input | Result |
|---|---|
| 12 April 1995 | 12 Dhu al-Qa'dah 1415 AH (Wednesday) |
| Age from 12 April 1995 to 22 October 2026 | 31 y 6 m 10 d Gregorian, 32 y 5 m 29 d Hijri, 11,516 days |
| 1 Ramadan 1448 AH | 8 February 2027 |
| 1 Muharram 1300 AH | 12 November 1882 |
| 1 Ramadan 1447 → 1 Ramadan 1448 | one Hijri year = 355 days |
Sources
Dates and rules on this page are checked against:
- Official Umm al-Qura Calendar · Kingdom of Saudi ArabiaThe official table of Hijri month starts
- The Umm al-Qura Calendar of Saudi Arabia · R. H. van Gent, Utrecht UniversityDetailed study of the calendar rules over time
- Islamic Calendar Types · Unicode CLDRDefines the islamic-umalqura calendar used by browsers
- UmAlQuraCalendar Class · Microsoft LearnUmm al-Qura support in Microsoft software
- Tabular Islamic calendar · WikipediaThe arithmetic calendar and the "Kuwaiti algorithm" in Windows
- Gregorian calendar · WikipediaMonth lengths and the leap year rule
If you find a result that disagrees with an official source, please contact us.