How the Hijri Calendar Works: The Lunar Year Explained Simply

The Hijri calendar is one of the simplest calendars ever used — and one of the most misunderstood. People often assume it is complicated because the dates “move”. In fact it moves precisely because it is simple: it follows the moon and nothing else.

This guide explains the mechanics in plain language: what a Hijri day, month and year are, how a month begins, why there are different versions of the calendar, and how to think about a Hijri date in everyday life.

The one rule: a month is one cycle of the moon

Every Islamic month begins with a new crescent moon and lasts until the next one. The Quran ties the calendar directly to the moon: “They ask you about the new moons. Say: they are markers of time for people and for Hajj” (2:189). Another verse says Allah made the moon in phases “so that you may know the number of years and the reckoning [of time]” (10:5).

The time from one new moon to the next — the synodic month — averages 29.53 days. You cannot have half a day in a calendar, so Hijri months are either 29 or 30 days long. There is no 28-day or 31-day month, and no month is fixed in length the way February always has 28 or 29 days.

Twelve months make a year — and the year is short

The Hijri year has twelve months (Quran 9:36). Twelve lunar months come to about 354.37 days, so a Hijri year has 354 or 355 days. That is roughly 11 days shorter than the 365-day solar year.

This single fact explains almost everything people find confusing:

• Ramadan begins about 11 days earlier each Gregorian year.
• Every Islamic month cycles through all four seasons in about 33 years.
• Someone aged 33 in Gregorian years is about 34 in Hijri years.

Hijri year	Approximate start (Umm al-Qura)	Length
1447 AH	26 June 2025	355 days
1448 AH	16 June 2026	355 days
1449 AH	6 June 2027	354 days

Notice the start date slides back by 10 or 11 days each year.

Why there is no leap month

The pre-Islamic Arabs did add a month every few years to keep their calendar near the seasons. The Quran ended that practice: “The postponement [nasi’] is an increase in disbelief” (9:37). Since then the Islamic calendar has been purely lunar.

There is a practical benefit to this. Because Ramadan moves through the seasons, no community is permanently stuck with summer fasts and no community always gets short winter days. Over a lifetime, everyone fasts in every season.

The day begins at sunset

In the Hijri calendar the day begins at sunset (Maghrib), not midnight. The night comes before its day. So the “night of the 27th” of Ramadan is the night that begins at sunset at the end of the 26th day.

This matters in two common situations:

• Ramadan: the first taraweeh prayer happens on the evening before the first fast.
• Special nights: if a website says the 15th of Sha’ban is a Saturday, the night of the 15th began on Friday evening.

Calendar converters, including ours, convert the civil day (midnight to midnight). If it is after sunset where you are, many people would already consider it the next Hijri date.

How a month begins: sighting and calculation

Here is where the calendar becomes a matter of method rather than mathematics. There are three main approaches in use today.

1. Local moon sighting

On the evening of the 29th day of a month, people look for the thin new crescent just after sunset. If it is seen, the new month starts at that sunset. If it is not seen — because of clouds, haze, or because the moon is too young — the current month completes 30 days. This follows the hadith: “Fast when you see it and stop fasting when you see it; if it is hidden from you, complete the count of thirty” (Sahih al-Bukhari 1909; Sahih Muslim 1081).

Because the crescent becomes visible on different evenings in different places, two countries can begin a month a day apart. Both can be following the method correctly.

2. A calculated calendar (Umm al-Qura)

Saudi Arabia publishes the Umm al-Qura calendar, which fixes the start of every month in advance using astronomical criteria for Makkah. It is the official calendar for civil life in Saudi Arabia and the one most Hijri websites show. For religious occasions — Ramadan, the Eids and Hajj — Saudi Arabia still announces dates after the moon is sighted, which usually but not always matches the calendar.

3. The tabular (arithmetic) calendar

Historians and software also use a fixed tabular calendar: months alternate 30 and 29 days, and 11 years in every 30 get an extra day. It never needs observation and is identical everywhere. It is useful for history and quick conversions, but it often runs a day — occasionally two — behind the observed months.

Our converter lets you switch between Umm al-Qura and tabular so you can see exactly where they differ.

Counting years: the Hijrah epoch

Hijri years are counted from the year of the Hijrah, the Prophet’s migration from Makkah to Madinah. The first day of the calendar, 1 Muharram 1 AH, corresponds to 16 July 622 in the Julian calendar used in Europe at the time. “AH” stands for Anno Hegirae, “in the year of the Hijrah”.

Because Hijri years are shorter, the Hijri count gains on the Gregorian count. In 622 the gap was 621 years; today it is 578 (2026 − 1448). The two counts will meet in around the year 20874 — a fun fact, but not something anyone needs to plan for.

A quick way to estimate the Hijri year

For a rough answer you can do in your head:

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

For 2026: (2026 − 622) × 33 ÷ 32 = 1447.9, which correctly points to 1447 turning into 1448 during 2026. For exact day-level conversion you need a proper algorithm or the converter — the estimate can be off by a few months.

Reading a Hijri date

A Hijri date is written day, month, year, followed by AH or (in Arabic) هـ:

• English: 4 Jumada al-Ula 1448 AH
• Numeric: 04/05/1448
• Arabic: ٤ جمادى الأولى ١٤٤٨ هـ

The month number in the numeric form is its position in the year: 05 is Jumada al-Ula, the fifth month. The Hijri date today page shows the current date in all of these formats with copy buttons.

Why your phone and your mosque might disagree

Your phone, a website and your local mosque can show different Hijri dates on the same day for three reasons:

1. Method: one uses Umm al-Qura, another the tabular calendar, another the local sighting.
2. Adjustment: many apps let users add or subtract a day to match local practice.
3. Time of day: after sunset, some people already count the next Hijri day.

None of these is an error. When it matters — for fasting, Eid or Hajj — follow the announcement your community follows. For everything else, a calculated calendar is close enough and has the advantage of being known in advance.

Living with a lunar calendar

Most Muslims use the Gregorian calendar for work and school and the Hijri calendar for worship. In practice, that means:

• Checking the Hijri date when an occasion approaches — the Islamic holidays page lists the next two years.
• Remembering that Islamic dates move about 11 days earlier each year, so last year’s Eid date is not this year’s.
• Knowing that the start of each month can be confirmed only near the time.

Understanding the one simple rule — a month is a moon — makes the rest of the calendar fall into place.