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Any two dates

Age Calculator down to the day

Years, months and days — plus the totals people ask for: how many weeks, how many hours, which weekday it was, and how long until the next birthday.

Short answerLast edited October 31, 2026

The Age Calculator gives an exact age in years, months, days and hours between a birth date and any date you pick. It counts in the calendar rather than dividing days by 365, so leap years and month lengths are handled correctly.

How it works

1

Enter the birth date

Add the day, month and year.

2

Set the date to measure to

Today, or another date if you are checking a record.

3

Read the age

See it in years, months and days.

3 date fieldsBirth, today, any target date
Leap daysCounted where they fall
Milestones10,000 days and half birthdays
Nothing storedCalculated in your browser
Count the days, not the years: the days are what you have.
A line worth taping to the fridge
  • Invoices, forms and visa applications that ask for an exact age
  • Baby and toddler ages, where the months matter
  • Retirement dates and pension planning
  • Celebrating round numbers — 10,000 days is a good excuse

Milestones and how they are counted

MilestoneDaysHow it is usually marked
First birthday365 or 366The calendar date, not 365 days
1,000 days1,000Roughly 2 years and 9 months
10,000 days10,000Around the 27th birthday
18,250 days18,250About 50 years
Leap day birthdayVariesUsually celebrated on 28 February or 1 March
How is the exact age counted?
Full years first, then full months since the last birthday, then the remaining days. That is the same order a passport office uses.
What about people born on 29 February?
The next birthday falls in the following year and the countdown uses the real calendar, so 29 February is counted when it exists.
Can I count the age at a past date?
Yes. Set the second field to any date and the answer is the age on that day.
Are working days subtracted?
No. The totals are calendar days, including weekends and holidays.
Why are weeks not exactly days ÷ 7?
They are: the week figure is the day total divided by seven and rounded down.

Why Exact Age Is Harder Than It Looks

Subtracting two dates sounds trivial until February arrives. Months have different lengths, leap years add a day and "one month older" depends on which month you mean.

The rule that works

Compare the day of the month first. If the target day is smaller, borrow the length of the previous month — which is exactly what this tool does, and what makes 31 January to 1 March two days short of a full month.

Age in law

Age is not a duration; it is a status that changes on your birthday at midnight in the timezone where you were born. Legal systems almost always count the two birthdays, not a number of days, which is why the calendar date decides.

Age in medicine

Paediatricians count in weeks and months up to two years, because growth is fast. After that, years are enough. Interesting, but hardly a reason to worry about a three-week correction.

Age in practice

Use the exact figure when a form demands it, and use the friendly one with your friends. If you are curious about the rest of the numbers that describe a body, the BMI calculator and the calorie calculator use exactly one of these fields.

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Quick facts

  1. An age in days is not exactly 365.25 times the years, because leap days fall in blocks and the gaps between birthdays differ.
  2. Age in months and days depends on the month lengths, which is why two people born on the same date can differ by a day in some years.
  3. The SI defines the kilo as exactly 1000 and the centi as exactly one hundredth, which is why conversions are exact, not approximate.BIPM
  4. Since 2019 the kilogram is defined by a fixed value of the Planck constant, not by a metal cylinder in Paris.BIPM

Questions people ask

How do I calculate my exact age in years and days?
Enter your birth date and the date you want to measure to. The calculator counts full years first, then the remaining months and days in the calendar. It is the same method used on official forms, not an estimate from total days.
How do you calculate age in days?
Count the days between the two dates, including the leap days that fall in between. A year has 365 days, or 366 in a leap year, so dividing the total days by 365.25 gives only an approximate number of years.
How many days until my next birthday?
Count from the date you are measuring to the next occurrence of your birth month and day. If that date has already passed this year, use next year. The Age Calculator shows the count in days when you enter a target date.

What this page is about

  • SI units

    The International System of Units maintained by the BIPM, with the metre, kilogram, second and their prefixes defined exactly.

Official sources cited on this page

  1. The International System of Units (SI Brochure)BIPM

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