Everyday tool
Age Calculator
Choose a birth date and an “as of” date to see completed years, months and days, plus total weeks, total days and the next birthday.
How exact age is calculated
The calculator starts at the birth date and adds whole months until the next month would pass the “as of” date. What remains is the number of days. This avoids the common bug where subtracting dates produces a negative day value.
For example, someone born on 31 January and measured on 1 March has completed one month and one day, not “one month and negative two days”. The month anchor is clamped to the last valid day when a month is shorter.
Leap years and month lengths
February has 28 or 29 days depending on the year. Months have different lengths. The calculator handles those differences and uses UTC dates internally so daylight-saving changes do not shift the result. A 29 February birthday is treated as 28 February in non-leap years when calculating the next birthday countdown.
What the totals mean
- Total months is the number of complete months between the two dates.
- Total weeks is total days divided by seven, rounded down.
- Total days is the exact number of calendar days between the dates.
- Next birthday is the next occurrence of the birth month and day on or after the “as of” date.
Date-only, not time-of-day
The inputs are calendar dates, not timestamps. If you need an age in hours or minutes, this is not the right tool. The result also does not account for time zones at the moment of birth; it treats both dates as calendar dates.
Keep going
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Good to know
Questions
Why are the days never negative?
The calculation anchors to completed months first, then counts the remaining days. That keeps years, months and days consistent instead of subtracting raw day numbers.
Does it handle leap years?
Yes. It accounts for 29 February and for months with different lengths. The next-birthday countdown clamps 29 February to 28 February in non-leap years.
Can I calculate age on a future date?
Yes. Change the “as of” date. This is useful for planning, eligibility dates or project timelines.
Is this legal or medical advice?
No. It is a date calculator. For legal age requirements or medical decisions, use the rules and advice that apply to your situation.
Can I calculate the gap between two dates, not just from a birth date?
Yes. Enter the earlier date as the date of birth and the later date as the “as of” date. The next-birthday line will be based on the earlier date.
How is age calculated for a 29 February birthday?
In non-leap years the next birthday is treated as 28 February. The result uses calendar dates in UTC to avoid daylight-saving drift.