Calculate exact age in years, months, and days from a birth date to today, plus total days, weeks, and days until the next birthday. Private and in-browser.
Runs entirely in your browser — your data never leaves your device.
How to use Age Calculator
What it does & when you need it
You need an exact age — for a form, a legal check, a "how long since launch"
figure, or just curiosity — and rounding "this year minus that year" is not good
enough. This tool takes a birth (or start) date and measures it against today,
returning the span in calendar-correct years, months, and days, along with the
total days and weeks lived and a countdown to the next birthday. It all runs in
your browser against your device's local date, so nothing you enter is uploaded.
How to use
Pick a date of birth with the date field, or press Sample to load one.
Read the breakdown in the output: years, months, and days, plus total days,
total weeks, total months, and days until the next birthday.
Press Copy result (or Ctrl/Cmd + Enter) to copy the summary.
Things worth knowing
Calendar units, not averages. The tool counts whole years, then whole months,
then leftover days, borrowing from the real preceding month rather than assuming
30-day months. That is why a span can read "1 month and 23 days" — the leftover
days depend on how long the months you crossed actually were, including February.
Leap years are handled. A 29 February birth date is accepted. In ordinary
years, which have no 29th, the anniversary is treated as 28 February for the
countdown; in a leap year the exact date returns and the age shows clean whole
years. This is the same convention most official calculators use.
It flips on your birthday, not New Year's. Because the calculation compares
month and day, the year count only increases once your birthday has passed, and
"next birthday in days" reads 0 on the day itself. The figures depend only on the
date, not the time or timezone, so they advance by one at each local midnight.
When you instead need a precise machine instant, convert with the
Unix timestamp converter or shift zones with the
timezone converter.
Examples
A date of birth
1990-05-20
Loads a birthdate; the tool shows years, months, and days plus totals against today in your timezone.
Leap-day birthday
2000-02-29
A 29 February birth date — see how the anniversary and countdown behave in non-leap years.
A recent start date
2020-01-01
Short spans still report total days and weeks, handy for the age of a project or an account.
Frequently asked questions
How are the years, months, and days worked out?+
It counts calendar units, not fixed averages: first the number of whole years between the two dates, then the whole months left over, then the remaining days. Because months differ in length and February gains a day in leap years, the day figure is computed by borrowing from the actual preceding month, so 15 Jan to 10 Mar is 1 month and 23 days, not a rounded guess.
What happens with a 29 February birthday?+
A leap-day birth date is valid and parsed correctly. In common (non-leap) years there is no 29 February, so the anniversary is clamped to 28 February for the countdown — the usual convention. On a real leap year such as 2024 or 2028 the exact anniversary lands on the 29th and the age shows whole years with zero months and days.
Why is the age not just this year minus my birth year?+
Subtracting years alone overstates your age until your birthday has passed this year. This tool checks the month and day: if today is earlier in the year than your birthday, it subtracts one from the year count and fills in the correct months and days, so the result flips on the birthday itself, not on 1 January.
Does the time of day or my timezone matter?+
No. The calculation works on whole calendar dates in your local timezone and ignores the time of day, so there is no daylight-saving or hour-of-day drift. The reference point is simply today’s date on your device, which is why the totals tick up by one each midnight.
What does “next birthday in days” count?+
It is the number of whole days from today until your next birthday, and it reads 0 on the birthday itself. It looks for the anniversary later this year and, if that date has already passed, rolls forward to next year, taking leap years into account along the way.