Days to Years, Months and Days Calculator
Convert a number of days into years, months and days — with fixed 365/30-day units, average calendar lengths, or exactly on the calendar from a start date — plus weeks, hours and the reverse conversion.
How it works
Fixed: years = ⌊days ÷ 365⌋, months = ⌊remainder ÷ 30⌋, days = what is left · Average: the same with 365.2425 and 30.436875 · Calendar: add the days to the start date and count whole years, months and days between the two dates · Decimal years = days ÷ 365.25 · Weeks = days ÷ 7
There are three sensible ways to turn a day count into years, months and days, and they can differ by a few days. The fixed method uses 365-day years and 30-day months: simple, easy to check by hand and the same every time. The average method uses the mean Gregorian year (365.2425 days, which accounts for leap years) and the mean month (one twelfth of that, about 30.44 days), so long spans come out closer to the calendar. The exact calendar method lays the days onto a real calendar from a start date you choose, so it knows which months have 28, 30 or 31 days and where the leap days fall — this is the one to use for contracts, notice periods or anniversaries. The reverse mode turns years, months and days back into a total day count with the same three choices. The table lists the span in weeks, decimal months and years, hours, minutes and seconds.
Worked example
400 days with fixed units: 400 ÷ 365 = 1 year, leaving 35 days; 35 ÷ 30 = 1 month, leaving 5 days, so 1 year, 1 month, 5 days. That is also 57 weeks and 1 day, or 400 ÷ 365.25 = 1.095 years. On the calendar from January 1, 2026, 400 days later is February 5, 2027: exactly 1 year, 1 month and 4 days, because January has 31 days rather than 30. In reverse, 1 year, 1 month and 5 days with fixed units is 365 + 30 + 5 = 400 days.
Frequently asked questions
Why do the methods give slightly different answers?
Real months are 28 to 31 days long and every fourth year (roughly) has 366 days. The fixed method ignores that for simplicity, the average method smooths it out, and the calendar method uses the actual months between your dates. For a quick feel use fixed; for a date-exact answer use the calendar method.
How many years is 1,000 days?
With fixed units, 1,000 days is 2 years, 9 months and 0 days (730 + 270). In decimal years it is 1,000 ÷ 365.25 ≈ 2.74 years. On the calendar it depends on the start date: from January 1, 2026 it is 2 years, 8 months and 26 days (ending September 27, 2028).
How many months is 180 days?
Exactly 6 months with 30-day months, about 5.91 average months (180 ÷ 30.44). On the real calendar half a year is 181 to 184 days, depending on which months it covers.
How do I convert years, months and days back to days?
Choose “Years, months, days → days”. With fixed units the total is years × 365 + months × 30 + days. With the calendar method the calculator adds the span to your start date and counts the actual days, so leap years and month lengths are included.
Does the calendar method count the start date?
No. It adds the days to the start date the way a date calculator does: 1 day after March 1 is March 2. The weekday count covers the days after the start date up to and including the end date.
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This calculator is for educational purposes. Double-check important results before acting on them.