Hijri and Gregorian calendars explained
Updated 30 October 2026 · 7 minute read
Two calendars run side by side in daily life for most Muslims. The Gregorian calendar is solar: its year follows the earth around the sun and stays aligned with the seasons. The Hijri calendar is lunar: its months follow the phases of the moon. The two drift against each other by about eleven days every year, which is why Ramadan moves steadily earlier through the seasons.
A year of 354 or 355 days
Twelve lunar months of 29 or 30 days add up to 354 or 355 days — roughly eleven days fewer than the 365 or 366 days of a solar year. Over about 33 solar years, the Islamic calendar completes a full cycle through the seasons.
Each month begins with the sighting of the new crescent, and in practice a month lasts either 29 or 30 days. There is no 31st day in any Hijri month, and no leap day in the Gregorian sense.
The twelve months
| # | Month | Common significance |
|---|---|---|
| 1 | Muharram | New year; Ashura on the 10th |
| 2 | Safar | — |
| 3 | Rabi al-Awwal | Birth month of the Prophet ﷺ (12th) |
| 4 | Rabi al-Thani | — |
| 5 | Jumada al-Ula | — |
| 6 | Jumada al-Akhirah | — |
| 7 | Rajab | 27th night (Isra and Mi’raj) |
| 8 | Shaban | 15th night; preparations for Ramadan |
| 9 | Ramadan | Fasting month |
| 10 | Shawwal | Eid al-Fitr on the 1st |
| 11 | Dhul Qadah | — |
| 12 | Dhul Hijjah | Hajj (8th–13th); Eid al-Adha on the 10th |
Three ways to decide where a month starts
This is the part that causes confusion, and it is not a calculation error. Different communities use different rules:
- Local sighting. A committee announces the start of the month after seeing the crescent with the naked eye or optical aid. Because the moon is not visible everywhere on the same evening, neighbouring countries can begin on different days.
- Calculated calendars. A fixed arithmetic or astronomical rule decides the date in advance. The Umm al-Qura calendar used in Saudi Arabia is the best-known example: it is calculated years ahead, so Saudi civil documents, bank systems and school calendars can be planned.
- Following a regional authority. Some countries and communities follow the announcement of a nearby country or a body such as the sighting authority they trust.
None of these is a mistake. They are different interpretations of the same instruction to begin the month with the new moon, and the difference at the start and end of a month is usually a single day.
What the converter does
Our Hijri converter uses the Umm al-Qura calendar through your browser’s built-in internationalisation data. Gregorian to Hijri is a direct formatting of the date; Hijri to Gregorian searches day by day until the requested Hijri date is found, and tells you if the day does not exist — for example asking for 30 Shaban in a year when Shaban has only 29 days.
Because the rule is fixed, the same input always produces the same output. That is what makes it useful for planning: an appointment, a deadline or a school term can be given in both calendars.
Examples for 1447–1448 AH
| Hijri date | Umm al-Qura Gregorian date |
|---|---|
| 1 Muharram 1447 | 26 June 2025 |
| 1 Ramadan 1447 | 18 February 2026 |
| 1 Shawwal 1447 (Eid al-Fitr) | 20 March 2026 |
| 10 Dhul Hijjah 1447 (Eid al-Adha) | 27 May 2026 |
| 1 Muharram 1448 | 16 June 2026 |
Your local mosque may announce Eid one day before or after these dates. Treat the table as the calculated calendar, not as an official announcement.
How to use dates correctly
- For worship and festivals, follow your local sighting authority. The calculator is a planning aid.
- For contracts and official forms in Saudi Arabia, Umm al-Qura is the civil reference.
- Write both dates in business documents when your customer is used to the other calendar — it removes ambiguity, especially around month-end.
- Remember the eleven-day drift when planning annually: a Hijri anniversary arrives about eleven days earlier each Gregorian year.