Does Ramadan move forward or backward?

Backward against the Gregorian calendar — about eleven days earlier each year, because the lunar year is shorter. Over roughly 33 years it works its way through every season and returns to where it started.

Is the Hebrew calendar lunar?

Lunisolar. Its months follow the moon, but it adds a thirteenth month seven times in every nineteen years to keep Passover in the spring. Only the Islamic and Hawaiian reckonings on this site are purely lunar.

Why not just add a leap month to the Islamic calendar?

Intercalation was practiced in pre-Islamic Arabia and was explicitly discontinued, so the twelve-month lunar year is a religious commitment rather than an unsolved arithmetic problem.

Why the Islamic calendar drifts through the seasons

Why the Islamic calendar drifts

Ramadan moves about eleven days earlier each year while the Hebrew and Chinese new years stay put. The reason is one design decision, made deliberately.

The short answer

A lunar year of twelve moons is about 354 days — roughly eleven days shorter than the solar year. The Islamic calendar keeps those twelve months and lets them drift, so Ramadan travels backwards through the seasons and returns to the same place after about 33 years. The Hebrew and Chinese calendars are also built on moons, but they add a whole leap month every few years to haul themselves back into step with the sun. That single choice — drift, or correct — is the whole difference.

The arithmetic behind the drift

A lunation — new moon to new moon — averages 29.53 days. Twelve of them come to 354.37 days. A tropical year, the sun’s round trip through the seasons, is 365.24 days. The gap is not subtle:

Year	Length	Against the solar year
Lunar (12 lunations)	354.37 days	10.88 days short
Tropical (solar)	365.24 days	—
Lunisolar, common year	353–355 days	short, and corrected later
Lunisolar, leap year	383–385 days	long, and that is the correction

Eleven days a year compounds. Thirty-three lunar years take about thirty-two solar ones, which is why a Muslim who fasts Ramadan for a lifetime experiences it in every season.

Drift is a decision, not an oversight

It would be easy to read the drift as a flaw someone failed to fix. It is the opposite. The Islamic calendar is deliberately untethered from the solar year, so its observances are not tied to a season — Ramadan in high summer and Ramadan in midwinter are both ordinary.

A calendar that has to keep an agricultural year cannot afford that. Planting and harvest are solar events, so any calendar used to schedule them must be pinned to the sun, whatever it does with the moon.

The lunisolar compromise

A lunisolar calendar wants both: months that begin at the new moon, and a year that stays with the seasons. The two are incompatible, so it cheats — periodically inserting a thirteenth month to absorb the accumulated shortfall.

The Hebrew calendar does this seven times in nineteen years, on the Metonic cycle — nineteen solar years being almost exactly 235 lunations. The Chinese calendar reaches the same end by a different route, inserting a leap month whenever one is needed to keep the solstice in the eleventh month.

Lunar — twelve moons, no correction, drifts about eleven days a year.
Lunisolar — moon months, plus a leap month every few years to hold the solar year.
Solar — the year is the unit; months are administrative divisions of it, and the moon is ignored.

Common questions

Does Ramadan move forward or backward?: Backward against the Gregorian calendar — about eleven days earlier each year, because the lunar year is shorter. Over roughly 33 years it works its way through every season and returns to where it started.
Is the Hebrew calendar lunar?: Lunisolar. Its months follow the moon, but it adds a thirteenth month seven times in every nineteen years to keep Passover in the spring. Only the Islamic and Hawaiian reckonings on this site are purely lunar.
Why not just add a leap month to the Islamic calendar?: Intercalation was practiced in pre-Islamic Arabia and was explicitly discontinued, so the twelve-month lunar year is a religious commitment rather than an unsolved arithmetic problem.

Last reviewed August 12, 2026 · Spot an error?