Days to Months

How to convert days to months

Divide the days by 30.436875, the length of an average month:

months = days ÷ 30.436875

90 days ÷ 30.436875 = 2.96 months. The average comes from the Gregorian calendar: 400 years contain 146,097 days, or 365.2425 days a year, and a year has 12 months, so a month averages 30.436875 days. The result also shows weeks and years. To go the other way, multiply months by 30.44.

Days to months chart

Average months and calendar months

Calendar months are not all the same length: February has 28 days (29 in a leap year), four months have 30 and seven have 31. So “90 days” and “3 months” land on different dates depending on when you start, and rules that say one usually mean exactly that. From October 7, 2026, 90 days later is January 5, 2027, while 3 months later is January 7. To count calendar months from a date, use the date calculator; for the months and days between two dates, the days between dates calculator.

Ages, pregnancies and subscriptions

Babies’ ages are counted in weeks at first and then in months; 100 days is 3.29 months, or 14 weeks and 2 days. Pregnancy is counted in weeks from the first day of the last period, and its 280 days are 9.2 average months, which is why “nine months” and “40 weeks” both get used. Free trials and subscriptions are usually set in days — 30, 60 or 90 — and renew on a calendar date, so the number of months in between depends on which months they cross.

Common periods

Notice periods work the same way: a “30-day notice” ends 30 calendar days after it is given, which can be the same date next month or a day or two off, while a “one-month notice” ends on the same date of the next month. When a document gives the period in days, count days; when it gives months, count calendar months. Banks and lenders sometimes use a 30-day month and a 360-day year for interest; that is a convention for calculation, not the calendar. For years, see weeks to years; for days in seconds or hours, days to seconds.