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Calculating days to years is a conversion that never gets old. Learn the relationship between the two "astronomical" measurement units, the only ones that truly have reason to exist as the week is entirely arbitrary, and the month varies in length so much not to be trustworthy! Keep reading to learn:

  • What is a year, and how do we calculate the length of a year?
  • How to convert days to years;
  • An example of how to calculate days into years.

What is a year? How long is a year?

A year is the time Earth requires to complete a revolution around the Sun: after a year, our Planet finds itself in the same position relative to the Sun again. Every orbiting planet has a "year", but since we are still living only on Earth, we will restrict our interest to the terrestrial year.

How long is a year? Easy, 365 days. Sure?

No: a year is not an exact multiple of the day (meaning that when the Earth returns to the exact position of a year before, it will face in a different direction. Leaving this effect unaccounted for would lead to dramatic consequences: not so slowly, our calendars would be all over the place, with seasons exchanged, the duration of the day never matching the one of the year before, and so on. The solution? Literally a patch: every four years, we assume that Earth takes one day more to complete its journey around the Sun: that year is a leap year, and it has 366 days. The addition of this leap day, on the 29th February resets the calendar.

Converting days to years: calculations for and explanation

How do we calculate days into years? The conversion is fairly easy; simply follow a few steps:

  1. Calculate the average length of a year:
    • Count three times the duration of a "standard" year: 3×365 days=1, ⁣095 days3 \times 365\ \mathrm{days} =1,\!095\ \mathrm{days}.
    • Add the length of a leap year: 1, ⁣095 days+366 days=1, ⁣461 days1,\!095\ \mathrm{days}+366\ \mathrm{days} =1,\!461\ \mathrm{days}.
    • Divide the result by 44: 1, ⁣461 days/4=365.25 days1,\!461\ \mathrm{days}/4 = 365.25\ \mathrm{days}.
  2. Take the number of days you are converting, and divide it by the average duration of a year.
  3. The result is the corresponding time in years.

You can convert days into years, not considering the average length of a year, only if you are sure that the duration you are considering doesn't encompass a leap year.

Calculate years to days: how many sunrise are in a given time?

Converting years to days is a similar operation; however, it can be even more helpful. Days are a very "human-sized" measurement units, and unless their number grows excessively, they are easier to grasp than years.
To calculate the years-to-days conversion, take your time in years and multiply by 365.25365.25, the average duration of a year.

Example: how many years is 10,000 days?

Ten thousand days sound like a long span of time. How many years are there? Let's find out!

We already found the average length of a year: 365.25 days365.25\ \mathrm{days}. The only operation left to us is dividing the number of days by the average length of a year:

ny=nd365.25 days/year=10,000 days365.25 days/year=27.38 years\footnotesize \begin{split} n_\mathrm{y} &= \frac{n_\mathrm{d}}{365.25\ \mathrm{days/year}}\\[1.2em] &=\frac{10,\!000\ \mathrm{days}}{365.25\ \mathrm{days/year}}=27.38\ \mathrm{years} \end{split}

Between a third and a fourth of the average human lifespan: quite a lot!

Other commonly used time units converter

If you need to convert from one measurement unit for time to any other unit, worry not: we created a comprehensive suite of tools for all your needs. Try:

How do I calculate days into years?

To calculate days into years, follow these easy steps:

  1. Find the average length of a year: as there is a leap year every four years, we calculate it with the following formula: (365 × 3 + 366)/4 = 365.25.
  2. Divide the number of days of your interest by the duration of the average year: you will find a decimal number: this is the number of years corresponding to the specified number of days.

The integer part of the result is the number of full years, while the decimal part corresponds to a fraction of a year.

How many years is 1,000 days?

1,000 days correspond to 2.738 years. To find this result:

  1. Take the number of days of your interest, in this case, 1,000 days.
  2. Divide it by the average year length (365.25 days): 1,000 days/365.25 days/year = 2.738 years.
  3. The integer part of the result is the number of complete years in the specified number of days.
  4. The decimal part, in this case, 0.738, is a fraction of the year: here, a bit more than 4/3 of a year.
Davide Borchia
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