Difference Between Two Dates, Hijri and Gregorian

Date conversion · 6 min read · Last updated: 29 October 2026

"How long has it been since this date?" or "how long until that appointment?" looks like a simple question, but the answer changes with the calendar and the unit you ask for. This article explains how to measure the gap between two dates correctly and when to use days and when months and years.

Days are the only fixed unit

The number of days between two dates is the same in any calendar, because a day is a fixed unit. Months and years have no fixed length: a Gregorian month is 28 to 31 days, a Hijri month 29 or 30, a Hijri year 354 or 355 and a Gregorian year 365 or 366. So you cannot divide days by 30 for months or by 365 for years except approximately.

A worked example in both calendars

Take the period from 15 March 2020 to 29 October 2026:

The period is the same, but the years and months differ because the Hijri year is shorter. Never compare a Hijri figure with a Gregorian one without knowing the calendar.

How years, months and days are counted

The method used is to subtract whole years first, then whole months, and the remainder is days, within the chosen calendar. When the second date's day is smaller than the first's, a month is borrowed using the length of the preceding month. That is why the gap between 31 January and 1 March cannot be called "one month" without a clear rule; the tool applies a fixed rule and always shows the total number of days next to it.

Steps in the tool

1. Open the date difference calculator.
2. For each date choose the calendar (Gregorian or Hijri) and enter day, month and year. You can mix calendars, one Hijri date and one Gregorian date.
3. Press calculate.
4. The period appears in days and in years, months and days in each calendar.

More worked examples

The third row shows that Ramadan 1448 has only 29 days; had we wrongly assumed thirty, we would have been a day out.

Common mistakes

• Treating a month as always 30 days: you will be a day or two out over long periods.
• Mixing Hijri and Gregorian in one calculation without converting.
• Forgetting the first day: do you count the start day or not? The difference between two dates subtracts the first from the second, so the start day is not counted.
• Relying on estimates: for legal deadlines (waiting periods, time limits, contracts) follow the official text on how days are counted, which may differ from the general calculation in your country.

When to use weeks

For short periods and projects, weeks are better because they are fixed at 7 days. 2,419 days is 345 weeks and 4 days. For ages and long subscriptions use years and months in the calendar that the relevant body specifies.

How to check your result

1. Count the days and compare with what the tool shows.
2. Add the computed period to the first date and you should land on the second.
3. If you calculated in both calendars, expect equal days and different months.

Common questions

Why does the tool's month count differ from mine by hand? Months can be counted in different ways when the day numbers differ. The tool adds whole months to the first date and then counts the remaining days, and shows the total days so you can check.

Can I calculate to a future date? Yes, and the result shows the days remaining. If the future date is Hijri, remember it is calculated and may change by a day with the announcement.

What range is supported? Gregorian dates from 1900 to 2076 and Hijri dates from 1318 to 1500 AH.

For a full age in both calendars use the age calculator, and to convert a single date the date converter. Remember that Hijri results are calculated by Umm al-Qura and may differ by one day from your country's date (why?).