How to Convert Gregorian to Hijri by Hand (With Worked Examples)

Online converters are quick, but there are times you want to understand — or check — the arithmetic yourself: a historical date in a book, a document with a Hijri expiry date and no internet, or simple curiosity. This guide gives you three methods, from a ten-second estimate to an exact conversion, with worked examples.

Method 1: the ten-second estimate (year only)

Because 32 Gregorian years are almost exactly 33 Hijri years, you can estimate the Hijri year with:

Hijri year ≈ (Gregorian year − 622) × 33 ÷ 32

And the reverse:

Gregorian year ≈ Hijri year × 32 ÷ 33 + 622

Example: what Hijri year is 2026? (2026 − 622) × 33 ÷ 32 = 1404 × 1.03125 = 1447.9

The answer near 1448 tells you that 1447 AH turned into 1448 AH during 2026 — which is right: 1 Muharram 1448 fell on 16 June 2026.

Example: what Gregorian year is 1400 AH? 1400 × 32 ÷ 33 + 622 = 1979.6, and indeed 1 Muharram 1400 fell on 21 November 1979.

Where the estimate goes wrong

The formula treats years as continuous. It cannot tell you the month, and around the turn of a Hijri year it can easily give the wrong year. For anything that matters — a contract, a document, a religious date — use one of the exact methods below.

Method 2: exact conversion using a reference date

The most reliable manual method is to count days from a date you know in both calendars. You need:

1. A reference date known in both calendars.
2. The number of days between the reference and your date.
3. The lengths of the Hijri months in between.

Step 1: choose a reference date

Pick a reference close to your target date to keep the counting short. Useful references on the Umm al-Qura calendar:

Gregorian	Hijri (Umm al-Qura)
16 June 2026	1 Muharram 1448
12 October 2026	1 Jumada al-Ula 1448
8 February 2027	1 Ramadan 1448
6 June 2027	1 Muharram 1449

The Hijri calendar 1448 page lists the start of every month, which gives you twelve reference points per year.

Step 2: count the days

Count the days from the reference to your date. A quick way is to count remaining days in the reference month, then add whole months, then the days into the final month.

Step 3: walk through the Hijri months

Add the same number of days on the Hijri side, month by month, using each month’s length (29 or 30).

Worked example: 15 October 2026 → Hijri

• Reference: 12 October 2026 = 1 Jumada al-Ula 1448.
• Days from 12 to 15 October: 3.
• 1 Jumada al-Ula + 3 days = 4 Jumada al-Ula 1448.

Short and exact. The work only grows when the gap crosses month boundaries.

Worked example: 25 December 2026 → Hijri

• Reference: 11 November 2026 = 1 Jumada al-Akhirah 1448.
• Days from 11 November to 25 December: 19 (rest of November, counting from the 11th) + 25 = 44 days.
• Jumada al-Akhirah 1448 has 29 days, so 29 days take us to 1 Rajab (which is 10 December 2026). 44 − 29 = 15 days remain.
• 1 Rajab + 15 days = 16 Rajab 1448.

Check: 1 Rajab = 10 December, and 10 + 15 = 25 December. ✓

Method 3: the tabular algorithm (exact, no reference needed)

If you have no reference dates, you can use the fixed tabular calendar, the same arithmetic that astronomers and software have used for centuries. It may differ from Umm al-Qura by a day or two, but it is fully self-contained.

The tabular calendar uses these rules:

• Months alternate 30 and 29 days, starting with Muharram at 30.
• In leap years (positions 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, 29 of each 30-year cycle), Dhul-Hijjah has 30 days.
• Day 1 (1 Muharram 1 AH) = Julian Day Number 1,948,440.

The procedure in outline:

1. Convert the Gregorian date to a Julian Day Number (JDN), the continuous day count used by astronomers. Any astronomy reference or spreadsheet function will do this; for 15 October 2026 the JDN is 2,461,329.
2. Subtract the epoch: 2,461,329 − 1,948,440 = 512,889 days have elapsed since 1 Muharram 1 AH.
3. Divide by 10,631 — the number of days in a 30-year cycle (30 × 354 + 11) — to count whole cycles: 512,889 ÷ 10,631 = 48 cycles, remainder 2,601 days.
4. 48 cycles = 1,440 years, so we are now at the start of 1441 AH. The remaining 2,601 days cover seven more years — 1441 to 1447, of which 1442, 1445 and 1447 are leap years — totalling 2,481 days. That leaves 120 elapsed days in 1448 AH.
5. Walk through the months of 1448 (tabular): Muharram 30, Safar 29, Rabi’ al-Awwal 30, Rabi’ al-Thani 29 → 118 days. Two more elapsed days put us on the 3rd of the fifth month: 3 Jumada al-Ula 1448 (tabular).

The tabular answer, 3 Jumada al-Ula, is one day behind the Umm al-Qura answer of 4 Jumada al-Ula. Differences of a day — occasionally two — between the two methods are normal, and are exactly why our converter lets you switch methods.

Converting Hijri to Gregorian

The same reference-date approach works in reverse.

Worked example: 10 Dhul-Hijjah 1448 → Gregorian

• Reference: 1 Dhul-Hijjah 1448 = 7 May 2027 (Umm al-Qura).
• 10 Dhul-Hijjah is 9 days after 1 Dhul-Hijjah.
• 7 May + 9 days = 16 May 2027.

That is the expected date of Eid al-Adha 1448.

Worked example: a Saudi document dated 15/03/1449

• 15/03/1449 means 15 Rabi’ al-Awwal 1449.
• Reference: 1 Rabi’ al-Awwal 1449 = 3 August 2027 (Umm al-Qura).
• 3 August + 14 days = 17 August 2027.

For Saudi documents, always use Umm al-Qura references: that is the calendar the government uses.

Finding the day of the week

The day of the week is the same in both calendars — 1 Ramadan 1448 and 8 February 2027 are the same Monday. So once you have the Gregorian date, any calendar gives you the weekday. If you are working with Julian Day Numbers, there is a neat shortcut:

Weekday = (JDN + 1) mod 7, where 0 = Sunday, 1 = Monday … 6 = Saturday

For 15 October 2026, JDN 2,461,329: (2,461,329 + 1) mod 7 = 4, so it is a Thursday.

Spreadsheet methods

If you have a spreadsheet open, you may not need to calculate at all.

• Microsoft Excel can display a date in the Hijri calendar using a number format beginning with B2 — for example, the format B2dd/mm/yyyy shows the Hijri date for any Gregorian date in the cell. Excel uses a tabular (Kuwaiti) algorithm, so results may differ by a day from Umm al-Qura.
• Google Sheets has no built-in Hijri format, but you can apply the 33/32 estimate with a formula, or paste in reference dates from our Hijri calendar 1448 page and count days with simple subtraction.

For contracts and documents, always confirm the spreadsheet result against an Umm al-Qura source.

Common mistakes to avoid

• Mixing calendars. Using a tabular reference with Umm al-Qura month lengths (or the reverse) gives errors of a day or two.
• Forgetting that Hijri months vary. Do not assume alternating 30/29 when you are working with Umm al-Qura; check the actual lengths.
• Counting the reference day twice. If 1 Rajab is 10 December, then 2 Rajab is 11 December — add one, not two.
• Ignoring the evening. The Islamic day begins at sunset. Converters give the civil date (midnight to midnight). If an event happened after sunset, its Hijri date may be the next day.

When to use which method

Need	Best method
“Roughly what Hijri year was 1950?”	33/32 estimate
Exact date for a Saudi document	Reference date with Umm al-Qura month lengths
A historical date from centuries ago	Tabular algorithm
Anything quick and important	The converter — and say which method you used

Doing a conversion by hand once or twice is the best way to understand why calendars and apps sometimes disagree. After that, let the converter do the counting.