Days in a Month Calculator

An average month is 30.436875 days, one twelfth of the mean Gregorian year of 365.2425. Nine months come to 273.93 days, twelve to exactly 365.2425. That is an average, not a calendar month: February has 28 or 29 days and July has 31.

This calculator scales a unit; it does not count a calendar. One month here is 30.436875 days — the mean Gregorian year of 365.2425 days divided by twelve, a division that leaves no remainder. Take the preset of 9 months: 9 × 30.436875 = 273.931875 days. Twelve months come back to exactly 365.2425, and half a month is 15.2184375. The arithmetic is linear, so twice the months is twice the days, and the answer depends only on the figure you type — never on which month you mean or which year it sits in. That is also the whole of what the calculator cannot do. It has no calendar, offers no month to pick, and cannot count a span from one date to another; the days-between-dates calculator is the tool for that. The limit that matters most is that the result almost never lands on a real calendar span. Already at twelve months it reads 365.2425 days, while the calendar only ever hands out 365 or 366 whole ones. The figure is an average over many years: good for turning a stretch of months into a rough number of days, unfit for fixing a date. The field takes 0 to 1200 months — a hundred years — with two decimals.