How Many Days Are in a Year? 365, 366 and 365.2425 Explained
The answer depends on which year you mean.
365 days
An ordinary calendar year has 365 days, which is 52 weeks and 1 day.
366 days
A leap year has 366 days, adding February 29. That's 52 weeks and 2 days.
365.2425 days
Averaged over the 400-year Gregorian cycle, a year is 365.2425 days. Use this for rough conversions such as "how many days is 20 years" (about 7,305 days).
Which to use
For exact answers between real dates, let the calendar decide. The date difference calculator counts the actual days.
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