To calculate your exact age, count the whole years from your birth date to today, then the whole months after that, then the days that are left over. So someone born on 20 May 1990, measured on 14 June 2026, is 36 years, 0 months and 25 days old. The age calculator does this in one step and also shows the totals in months, weeks, days and hours.
That is the whole method. Below is why each step works, and the two rules that trip people up.
The three-step method
Age is measured in three units that get smaller: years, then months, then days. You count the largest unit you can, then move down.
- Whole years. Count how many times your birthday has fully passed. If your birthday this year has not happened yet, you have not completed the current year, so do not count it.
- Whole months. From your most recent birthday, count complete months up to today.
- Leftover days. Count the days from there to today.
Working from largest to smallest avoids double counting and gives the same answer you would get by ticking off a calendar.
Why month lengths matter
A common shortcut treats every month as 30 days. That is where quick age maths goes wrong, because months are 28, 29, 30 or 31 days long. If a span crosses February or the end of a long month, the 30-day assumption drifts by a day or more.
Counting against the real calendar fixes this. The age calculator walks the actual months between your birth date and today, so a birthday in late January or a span across a 31-day month both come out exactly right.
The 29 February rule
If you were born on 29 February, your true birthday only exists in leap years. The usual convention is to treat 28 February as your birthday in common years, so you still age by a year on that date. This keeps the count moving every year rather than freezing it until the next leap year. The calculator uses this rule.
Your age in other units
Once you know the years, months and days, the same elapsed time can be shown other ways:
- Total months: whole years times twelve, plus the extra months.
- Total weeks and days: the total day count divided into weeks, with the remainder as days.
- Total hours: total days times twenty-four.
These totals are handy for milestones, such as spotting the day you turn 10,000 days old. Enter a birth date in the age calculator to see them all at once, along with the weekday you were born on and the countdown to your next birthday.
Where this comes up
Getting an exact age right matters most when a rule or a record depends on it:
- Forms and eligibility, where an age limit or a cut-off date applies on a specific day.
- Milestones, such as a 1,000-week or a 30-year mark you want to celebrate on the right date.
- Records and certificates, where the age must match the calendar exactly.
For the gap between any two dates rather than an age from today, see how many days between two dates, or open the age calculator to try it now.