Age Calculator
Find someone's exact age in years, months and days — or use it as a general date-difference calculator between any two dates.
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Related tools
Age is simple until you actually need the exact number — years, months, and days between two dates, not just "born in 1990." This calculator handles the month-length and leap-year math for you, and doubles as a general date-difference calculator for anything from a project deadline to an anniversary.
How exact age is calculated
This calculator counts complete years, then complete months within the current year, then whatever days are left over — the same way you'd count on your fingers, just handling every month's different length (28 to 31 days) and leap years automatically. That's different from simpler math like (today − birth date) ÷ 365.25, which gives a close estimate but drifts slightly depending on exactly where the leap years fall.
Using "Date difference" mode for anything other than age
Click "Date difference" above the fields to relabel them "From" and "To" instead of birth-date wording — handy for anything that has nothing to do with age, like how long a couple has been together, how many days until a contract renews, or how long ago a project launched.
Why age in days isn't just years × 365
Multiplying years by 365 undercounts by roughly one day for every four years, since about a quarter of years are leap years with 366 days. Over a 40-year span that adds up to around 10 missing days — small compared to a lifetime, but enough to throw off an exact day count, which is why this calculator works from actual calendar dates instead of a flat multiplier.
Leap years and other date quirks
Someone born on February 29 only has a real birthday once every four years; in the other three, this calculator treats it as falling on March 1, since that's the next real calendar day after where February 29 would have been. Every other calculation — total days, weeks, and months — is unaffected, since it always works from actual calendar dates rather than an approximation.
Frequently asked questions
Does this calculate my exact age, or an estimate?
Exact — it works from the real calendar dates you enter, counting complete years, months, and days rather than approximating with a flat 365-day year.
Can I use this to find the difference between any two dates, not just from a birth date?
Yes — switch to "Date difference" mode above the fields (it relabels them "From" and "To"), or just leave it on "Age" and enter any two dates directly. Either way the result is the elapsed time between them, whether that's how long a couple has been together or the gap between two project milestones.
Is my birth date sent to a server or stored anywhere?
No. Every calculation happens locally in your browser using plain date arithmetic — nothing you enter here is transmitted or saved.
Why doesn't my age in days match years × 365?
Because roughly a quarter of years are leap years with 366 days, not 365. This calculator counts actual calendar days rather than multiplying, so leap years are automatically included.
What happens if I set "Age at" to a date before the date of birth?
The calculator shows an error instead of a negative or nonsensical result — enter the earlier date as "Date of birth" and the later one as "Age at."
Does this handle a leap year birthday (February 29)?
Yes — in non-leap years, a February 29 birthday is treated as falling on March 1, the next real date after it, for the purposes of the next-birthday countdown.