Age Calculator
Enter your date of birth to see the day of the week you were born, exactly how old you are in years, months and days, and how long it is until your next birthday.
Pick a date to get started
Useful for checking how old someone was, or will be, on a particular day.
Dates are treated as whole calendar days, so time zones and clock changes never shift the answer.
Calculated as of today.
How to use this calculator
- Enter your date of birth. Type it straight into the field, or use the calendar button beside it — the year dropdown makes it quick to jump back decades.
- Read the weekday. The headline result is the day of the week you were born, with the full date underneath.
- Check your exact age in years, months and days, along with the totals in months, weeks, days and hours.
- Look at the birthday countdown. The result card shows how many days are left and what age you turn; the card below lists the next four birthdays and which weekday each falls on.
- Optionally pick a different reference date to work out how old someone was, or will be, on any other day.
How the maths works
Age is a calendar difference, not a simple subtraction of days, because months and years vary in length. The calculator works from the largest unit down:
- Count the largest number of whole years that still land on or before today.
- From that anniversary, count the whole months that fit.
- Count the days left over.
The totals are straightforward once the exact span is known:
total days = today − date of birth
total weeks = total days ÷ 7
total hours = total days × 24
months lived = years × 12 + months
The weekday comes from the Gregorian calendar itself. Because 400 years contain exactly 20,871 weeks, the pattern of weekdays repeats perfectly every 400 years — which is why a date and its weekday can always be matched up without a lookup table.
Worked examples
A birthday still to come this year
Born 25 December 1995, checked on 20 September 2026.
- Born on a Monday
- Age: 30 years, 8 months and 26 days
- Next birthday: 25 December 2026, a Friday, 96 days away
- Turning 31
A birthday that has already passed
Born 10 March 1995, checked on the same day.
- Age: 31 years, 6 months and 10 days
- The next birthday rolls into the following year:10 March 2027, turning 32
A leap-day birthday
Born 29 February 2000 — a Tuesday.
- 2027 is not a leap year, so that birthday falls back to 28 February 2027
- 2028 is a leap year, so the real date returns: 29 February 2028
- The age itself still advances every single year — only the date moves
Frequently asked questions
Every date in the Gregorian calendar maps to exactly one weekday, and the pattern repeats on a 400-year cycle. The calculator converts your date of birth to a fixed point on that calendar and reads the weekday straight off it.
There is no guessing involved: the same date always gives the same answer, and it accounts for leap years including the century rule that skips 1900 and 2100.
Age is counted from your birthday, not from the start of the calendar year. You turn a year older on the anniversary of your birth, so for part of every year your age and the difference between the two calendar years will not match.
The calculator counts whole years first, then whole months, then the days left over, which is how ages are worked out in everyday and legal use.
You keep the real date in a leap year, and in other years the calculator falls back to 28 February. That is the convention most of the English-speaking world uses for legal ages and birthdays.
Some places instead treat 1 March as the birthday in common years. If that matters for a legal deadline, check the rule that applies where you are.
Yes. Turn on "work out the age on another date" and set the second date to whatever day you are interested in — a wedding, an exam, a historical event, or a date in the future.
The age, the weekday and the countdown are all recalculated against that date instead of today.
It is, plus the extra months since your last birthday. Someone who is 30 years and 7 months old has lived 367 whole months, not 360.
Months are also not all the same length, which is why the calculator counts whole calendar months and then reports the remaining days separately rather than converting everything to an average month.
No. Dates here are treated as whole calendar days rather than moments in time, so a clock change, a daylight-saving shift or travelling across time zones never adds or removes a day.
The hours figure is simply the number of days multiplied by 24.