Persian, Islamic and Gregorian Calendars: How They Work and How to Convert Dates

On 19 October 2026, the day this guide was published, it was 27 Mehr 1405 in Iran and 8 Jumada al-Ula 1448 in Saudi Arabia’s official calendar. All three dates describe the same day, counted in three different ways. If you deal with documents from Iran or Afghanistan, plan around Ramadan or simply want to know your birthday in another calendar, it helps to understand how each system works.

The three calendars at a glance

The Gregorian calendar

Introduced by Pope Gregory XIII in 1582 to correct the drift of the older Julian calendar, the Gregorian calendar has 365 days with a leap day on 29 February. A year is a leap year if it is divisible by 4, except century years, which are leap years only if divisible by 400. So 2000 was a leap year and 2100 will not be. That gives 97 leap years every 400 years and an average year of 365.2425 days, very close to the solar year of about 365.2422 days.

The Solar Hijri (Persian) calendar

Iran’s official calendar is solar like the Gregorian one, but its year begins at the spring equinox. Nowruz, 1 Farvardin, is the day of the March equinox if the equinox occurs before noon Tehran time, otherwise the following day. Between 2000 and 2100 that is always 20 or 21 March. The present month lengths and the Persian month names were fixed by law in 1925.

Because the year is tied to the equinox, a Persian date falls on almost the same Gregorian date every year, which makes conversion predictable. To get the Persian year, subtract 621 from the Gregorian year after Nowruz and 622 before it: 19 October 2026 is in 1405, 1 January 2027 still in 1405 (11 Dey).

Leap years follow the astronomical equinox rather than a simple “every fourth year” rule. Most are four years apart, with an occasional five-year gap: 1399 and 1403 were leap years, the next ones are 1408 and 1412.

The lunar Hijri (Islamic) calendar

The Islamic calendar counts twelve lunar months of 29 or 30 days: Muharram, Safar, Rabi al-Awwal, Rabi al-Thani, Jumada al-Ula, Jumada al-Akhira, Rajab, Shaban, Ramadan, Shawwal, Dhu al-Qadah and Dhu al-Hijjah. A year has 354 or 355 days, about eleven days fewer than a solar year, so Islamic dates move through the seasons. Ramadan, for example, begins about eleven days earlier each Gregorian year:

Why an Islamic date can be off by one day

Traditionally a month begins when the new crescent moon is seen after sunset. Whether it can be seen depends on the weather and the place, and countries follow different rules: some rely on local sighting, some follow Saudi Arabia, some use astronomical calculation. A converter can only calculate, and two calculation methods are common:

• Umm al-Qura, Saudi Arabia’s official calendar for civil purposes. It is computed in advance: since 1423 AH (2002), a new month starts after the 29th day if the new moon occurs before sunset in Mecca and the moon sets after the sun.
• Tabular (civil), a purely arithmetic calendar with a 30-year cycle of 11 leap years, useful for historical dates.

The two methods can differ by a day. For 19 October 2026, our converter gives 8 Jumada al-Ula 1448 with Umm al-Qura and 7 Jumada al-Ula with the tabular method. For religious dates such as the start of Ramadan or Eid, always follow the announcement of your local religious authority.

How to convert a date reliably

Good converters don’t add or subtract months. They turn the date into a running day count, the Julian Day Number, which counts days continuously from 4713 BC, and then express that number in the other calendar. That avoids errors with month lengths and leap years.

1. Open the Date Converter (Persian, Hijri, Gregorian) and choose the calendar you are converting from.
2. Enter the year, then choose the month and the day; the lists always show the correct number of days for that month.
3. Read the date in all three calendars at once, with a note if the year is a leap year.
4. For Islamic dates, choose Umm al-Qura or the tabular method, and remember the possible one-day difference.

Date Converter (Persian, Hijri, Gregorian)Convert dates between the Persian (Solar Hijri/Shamsi), Islamic (Lunar Hijri) and Gregorian calendars, with weekday and leap years.Open tool

Common pitfalls

• Persian years across Nowruz. January to mid-March belong to the previous Persian year: 1 January 2027 is 11 Dey 1405, not 1406.
• Ages in lunar years. Because the Islamic year is shorter, 33 solar years are about 34 lunar years. Someone who turns 33 is already about 34 in the Islamic calendar.
• Counting days between dates. Count days, not months. The Date Difference Calculator gives the exact number of days between two dates, and the Age Calculator an age in years, months and days.
• Order and digits. Persian dates are usually written year/month/day and often with Persian digits: ۱۴۰۵/۰۷/۲۷ is 27 Mehr 1405.

Tools used in this guide

• Date Converter (Persian, Hijri, Gregorian)

  Convert dates between the Persian (Solar Hijri/Shamsi), Islamic (Lunar Hijri) and Gregorian calendars, with weekday and leap years.

  Open tool

• Date Difference Calculator

  Count the days between two dates, including weeks, business days (Mon–Fri) and the difference in years, months and days.

  Open tool

• Age Calculator

  Calculate your exact age in years, months and days, plus total weeks and days lived and the days until your next birthday.

  Open tool

Frequently asked questions

What year is it in the Persian calendar?

From Nowruz 2026 (21 March 2026) to 20 March 2027 it is 1405. After Nowruz, the Persian year is the Gregorian year minus 621; before Nowruz, minus 622.

When does Ramadan start in 2027?

According to the Umm al-Qura calculation, 1 Ramadan 1448 falls on 8 February 2027. The actual start can differ by a day, depending on the moon sighting and on the authority your country follows.

Why is my converted Islamic date one day off?

Islamic months traditionally begin with the sighting of the crescent moon, which a converter cannot know in advance. Calculated calendars such as Umm al-Qura and the tabular calendar can differ from each other and from the official date in your country by a day.

Is the Afghan calendar the same as the Persian calendar?

Both are Solar Hijri calendars with the same structure, but Afghanistan traditionally uses different month names, based on the signs of the zodiac (Hamal, Sawr, Jawza and so on).

How does your converter calculate dates?

For the Persian calendar it uses Kazimierz Borkowski’s algorithm, which is based on astronomical calculations of the equinox and matches the Iranian calendar for years 1 to 3177. For Islamic dates it uses the Umm al-Qura and tabular calendars built into your browser. All conversions go through the Julian Day Number.

Sources and further reading

1. Solar Hijri calendar – Wikipedia (en.wikipedia.org)
2. The Persian Solar Hijri calendar – timeanddate.com (www.timeanddate.com)
3. R. H. van Gent: The Umm al-Qura calendar of Saudi Arabia (Utrecht University) (webspace.science.uu.nl)