About how many days shorter is the Islamic year than the Gregorian solar year?

The Islamic year is about 10 to 11 days shorter than the Gregorian solar year.

A common Islamic year contains 12 lunar months of 29 or 30 days, totaling about 354 days. The Gregorian calendar follows the solar year, which averages about 365.24 days, so the difference is roughly 10.9 days. That gap causes Islamic dates to shift earlier through the Gregorian calendar each year.

Ramadan therefore does not stay in one season. Over a complete cycle of roughly 33 years, the month passes through the full range of seasons and returns to a similar time of year. This seasonal movement is a defining feature of the Islamic calendar.

The Islamic calendar does not regularly add a leap month to keep lunar months aligned with the solar year. By contrast, the Hebrew calendar is lunisolar and uses adjustments to preserve seasonal alignment. Gregorian leap years add a day, but they do not eliminate the larger difference between solar and lunar year lengths.