Age Calculator
Turn a date of birth and a target day — today unless you change it — into completed years, leftover months and leftover days, plus the exact number of calendar days lived. Leap-day birthdays clamp to 28 February in common years instead of skipping to 1 March.
How to use
- Enter the birth date. Invalid days such as 31 April are rejected, not rolled into May.
- Leave the target as today, or set a past or future date you want age “as of” (a census day, a school cut-off, a policy anniversary).
- Read years, then remaining months, then remaining days — and the total-days figure underneath.
- If the target is before the birth date the page will not invent a negative age. Use Birthday Countdown for “days until the next birthday,” not this tool.
How it works
Spoken age is not “total days ÷ 365.25.” People say they are 32 years and 4 months when they have completed 32 year-anniversaries and then 4 month-anniversaries, with some leftover days. This page follows that civil-calendar stacking. The year count drops back by one if this year’s anniversary has not arrived yet; months then walk from that last year-anniversary with the same clamp used when a month is shorter than the birth day.
Clamping is the rule that stops 31 January from becoming 3 March. Adding one calendar month to 31 January lands on the last day of February: 28 February in a common year, 29 February in a leap year. That span is one complete month and zero leftover days. The same clamp applies when someone is born on the 31st and you ask their age on a 30-day month.
A 29 February birthday is a special case of the same idea. In a non-leap year there is no 29 February, so the anniversary is treated as 28 February. Someone born on 29 February 2000 therefore turns 23 on 28 February 2023 on this page, not on 1 March. That matches how many civil registries treat the leap-day anniversary when the date does not exist.
Total days is a separate, exact count of midnights between the two dates. It includes every leap day that sits inside the span. It is not 365 × years, not 365.25 × years, and not a 30-day bank month. Use it when a form asks “days lived” or when you want to cross-check the stacked years-months-days breakdown.
The target must be on or after the birth date. Future targets are allowed — “how old will this child be on the first day of school” — and past targets answer “how old were they on that day.” Time of day is ignored; two people born on the same calendar date have the same age here regardless of birth hour. For a next-birthday countdown that waits for a real 29 February instead of clamping, use Birthday Countdown.
Formula
Age = completed years + remaining months + remaining days Total days = target date − birth date (in calendar days)
Worked examples
Whole years on an anniversary
born 2000-01-01, age at 2024-01-01 → 24 years, 0 months, 0 days (8,766 days)
Clamped January 31 anniversary
born 2023-01-31, age at 2023-02-28 → 0 years, 1 month, 0 days
Useful notes
- The target date must be on or after the birth date.
- Total days is an exact calendar-day count, not 365.25 × years.
- 29 February birthdays use 28 February as the anniversary in non-leap years.
FAQ
- How is age in months calculated when the birthday is the 31st?
The next month’s anniversary is the last day of that month if the 31st does not exist. 31 January to 28 February in a non-leap year is one complete month.
- What happens for a 29 February birthday?
In non-leap years the anniversary is 28 February, so someone born on 29 February 2000 turns 23 on 28 February 2023.
- Is the total-days figure exact?
Yes. It is the number of calendar midnights between the two dates, including leap days that fall in the span.
- Can I calculate age on a future date?
Yes. Change the target to the future day. The same year-month-day stack and leap-day clamp apply.
- Why is this different from dividing days by 365?
Dividing by 365 (or 365.25) ignores month lengths and leap-day anniversaries. This page uses completed calendar years and clamped month anniversaries, then leftover days.
Related tools
See all Date & Time tools.