How to calculate your age
Working out an exact age sounds trivial until you try it by hand. Months have different lengths, leap years add a day, and "how old am I" usually means age today rather than on your last birthday. Getting all three right is what turns a rough number into a precise years, months and days figure.
Your age is the amount of time between your date of birth and a reference date — usually today. The age calculator returns it in exact years, months and days; this guide explains how that is worked out and why the reference date matters.
How age is calculated
The reliable method compares the two dates piece by piece:
- Years. Subtract the birth year from the reference year.
- Months. Subtract the birth month. If the reference month is earlier in the year than the birth month, borrow a year (the last birthday has not happened yet this year).
- Days. Subtract the birth day. If the reference day is earlier in the month, borrow a month — using the actual number of days in the preceding month.
That borrowing step is where mental maths goes wrong, because the number of days you borrow depends on which month it is.
Why leap years and month lengths matter
Months range from 28 to 31 days, and February gains a 29th day every leap year. A naive "30 days per month" shortcut drifts by several days over a lifetime. An exact calculation uses the real length of each month, including the leap-year rule, which is why a tool is more trustworthy than an estimate for anything official.
Why the "age as of" date matters
Age is only meaningful relative to a date. The age calculator defaults to today, but you can set any reference date to answer questions like "how old will I be on this exam day" or "what age was I on that deadline". Eligibility rules — for school entry, jobs or documents — are almost always stated as an age on a specific cut-off date, so changing the reference date is what makes the tool useful for them.
Common uses
- Eligibility checks against an exact cut-off date.
- Forms and documents that ask for age in years and months.
- Counting down to a birthday or milestone.
If you only need the raw number of days between two dates, the date difference calculator is the simpler tool — see counting days between dates.
Frequently asked questions
Does the age calculator count leap years?
Yes. It uses the actual length of each month, including 29 February in leap years, so the days figure is exact.
Can I find my age on a future or past date?
Yes — set the "age as of" date to any day, and the age calculator works out your age on that date.
My birthday is stored in the Nepali (BS) calendar — what do I do?
Convert it to an AD date first using the BS to AD conversion guide, then enter the AD date of birth.
Calculate your age
Enter your date of birth in the age calculator to get your exact age now, or set a reference date to check it on any day. More date tools are in our date and time tools guide.
