It’s easy to convert days to years using simple arithmetic. Here is how you do the conversion, with worked example and a table of values.
Days and Years
Both days and years are two units of time. A day is the time for one complete rotation of the Earth around its axis, so it is one day and one night or 24 hours. A year is the time for one complete orbit of Earth around the Sun.
Converting between them gives approximate or rounded values. Over short spans of time, this is not important. For example, whether you call a day 365 days or 365.2425 (accounting for leap year) makes little difference in your answer most of the time. The difference does matter when you look at thousands of days or when you convert from years to days.
Days to Years Conversion Formula
There are three common conversion factors for the day to year conversion:
- 1 day = 365 days (rounded, but usually good enough)
- 1 day = 365.2425 (better, since it accounts for leap year)
- 1 year = 0.0027379 (accounts for leap year and makes math easy)
The conversion factors result in these easy conversion formulas:
- years = days ÷ 365
- years = days ÷ 365.2425
- years = days x 0.0027379
For the most part, it does not matter which formula you choose, although the second two are more accurate.
Days to Years Conversion Example
For example, convert 10,000 days to years.
Here are the values you get using each conversion formula:
- years = days ÷ 365 = 10000 ÷ 365 = 27.397
- years = days ÷ 365.2425 = days ÷ 365.2425 = 27.379
- years = days x 0.0027379 = days x 0.0027379 = 27.379
In all cases, you likely round to 27.4 or 27 days, so the answer is pretty much the same. However, if you need to know to the hour or minute when an event occurs, make sure you account for leap year. Even then, be aware the Gregorian calendar isn’t perfect. Over long spans of time, you’ll get more error in your answer.
How to Convert Years to Days
The years to days unit conversion works using the same conversion factors.
- days = years x 365 (least accurate)
- days = years x 365.2425 (better)
- days = years ÷ 365.2425
For example, find the number of days in 5 years:
days = years x 365.2425 = 5 x 365.2425 = 1826.21
Using the less accurate conversion, you’re off by a day:
days = years x 365 = 5 x 365 = 1825
Day to Year Conversion Table
This table lists day to year conversions. In some cases, the values are rounded.
| Days | Years |
|---|---|
| 1 | 0.0027379 |
| 2 | 0.0054758 |
| 3 | 0.0082137 |
| 4 | 0.010952 |
| 5 | 0.013690 |
| 6 | 0.016427 |
| 7 (1 week) | 0.019165 |
| 8 | 0.021903 |
| 9 | 0.024641 |
| 10 | 0.027379 |
| 90 | 0.24641 |
| 100 | 0.27379 |
| 200 | 0.54758 |
| 365 (about 1 year) | 0.99934 |
| 550 | 1.5058 |
| 735 | 2.0124 |
| 915 | 2.5052 |
| 1000 | 2.7379 |
| 2000 | 5.4758 |
| 5000 | 13.690 |
| 10,000 | 27.379 |
| 100,000 | 273.79 |
| 1,000,000 | 2737.91 |
References
- Blackburn, Bonnie; Holford-Strevens, Leofranc (2003). The Oxford Companion to the Year: An Exploration of Calendar Customs and Time-Reckoning (corrected reprinting of 1999 ed.). Oxford University Press. ISBN 9780192142313.
- Duncan, D. E (1999). Calendar: Humanity’s Epic Struggle To Determine A True And Accurate Year. HarperCollins. ISBN 9780380793242.
- Morrison, L. V.; Stephenson, F. R. (2004). “Historical values of the Earth’s clock error ΔT and the calculation of eclipses”. Journal for the History of Astronomy. 35, part 3 (120): 327–336. doi:10.1177/002182860403500305
- Swerdlow, N. M. (1986). “The Length of the Year in the Original Proposal for the Gregorian Calendar”. Journal for the History of Astronomy. 17 (49): 109–118. doi:10.1177/002182868601700204