Years to Days Converter

What this converter does

This turns a number of years into days. Since a year is not a whole number of days, it uses an average year, so the result is a close estimate. Enter the years and the days come straight back.

How to use it

1. Enter Years. Type the number of years.

Press Calculate and the equivalent in days appears.

The 365.25-day year

The conversion multiplies by 365.25, the average length of a year in days. A common year is 365 days, but every four years a leap day is added to keep the calendar in step with the seasons, and spreading that extra day across four years adds a quarter of a day to each on average. So 365.25 days is the average year once leap years are counted in, which is why it is used here rather than a flat 365.

Why the quarter day works out exactly

The quarter day is not just a fudge, and there is a neat way to see it. Take any four-year span with one leap year in it. That is three years of 365 days plus one of 366, which adds up to 1,461 days. Divide that by 4 and you get exactly 365.25. So while no single year is 365.25 days, four years really are 1,461 days, and the average is dead on across that cycle. The estimate only drifts when your span has more or fewer leap years than one in four, which is where the small wobble comes from.

An example

Take 1 year. Multiply by 365.25 and you get about 365.25 days. Four years is exactly 1,461 days, and 10 years is about 3,652.5. For a round figure, a decade is roughly three and a half thousand days.

Questions people ask

How many days are in a year?

365 in a common year and 366 in a leap year, averaging 365.25. This converter uses that 365.25 average.

Why 365.25 and not 365?

Because of leap years. Adding a leap day every four years adds a quarter day per year on average, giving 365.25.

Are four years exactly 1,461 days?

Yes, for a span with one leap year: three years of 365 plus one of 366 is 1,461, which is exactly four times 365.25.

How do I go from days back to years?

Divide the days by 365.25, or use a days-to-years converter, which uses the same average.

References

1. U.S. Naval Observatory, Astronomical Applications Department: Leap Years. https://aa.usno.navy.mil/faq/leap_years