Age Calculator by Date of Birth

Enter a date of birth to see the exact age today — or on any other date — in years, months and days, plus total months, weeks, days and hours. The calculator also shows the day of the week you were born, how many days until your next birthday, and when you reach milestones like 10,000 days or a billion seconds.

How age is calculated

Age in years, months and days counts complete years first, then complete months, then the remaining days — the same way you would count on a calendar. If the day of the month hasn’t been reached yet, one month is borrowed and the days are counted from the same day in the previous month. Totals in weeks, days and hours count every calendar day between the two dates.

What the calculator shows

How to use it

1. Enter the date of birth.
2. Leave “Age on date” as today, or change it to find an age on a past or future date — for school entry, retirement or an event.
3. Optionally add a time of birth for the billion-seconds milestone.
4. Read the age, totals, next birthday and milestone table.

Worked example

Someone born on 15 June 1995 is, on 29 September 2026, 31 years, 3 months and 14 days old — 11,429 days, or 1,632 weeks and 5 days. They were born on a Thursday, and their next birthday is on 15 June 2027, 259 days away. They passed 10,000 days old on 31 October 2022.

Leap-year birthdays

People born on 29 February celebrate on 28 February or 1 March in non-leap years, depending on custom and local law. For legal age calculations, many jurisdictions treat the birthday as 1 March in common years; others use 28 February. The calculator shows 1 March as the next birthday in non-leap years and counts exact days either way.

Age in other traditions

Some cultures count age differently. In the traditional East Asian system, a baby is one year old at birth and everyone gains a year at the new year. South Korea officially adopted the international “full age” for legal purposes in 2023, but traditional counting is still used socially. This calculator uses international full age.

Age in months and weeks for babies

For babies and toddlers, age is usually counted in weeks and months rather than years — growth charts, feeding advice and developmental milestones are organised that way. The total weeks and months results give these figures directly. Health visitors and doctors sometimes use “corrected age” for premature babies, which subtracts the number of weeks the baby was born early; subtract those weeks yourself if you need it.

Checking an age for a form

Forms often ask for your age “as of” a particular date — for example on 31 December of the application year, or on the first day of a competition. Set the “Age on date” field to that date and use the years figure. If the form asks for age in completed years, ignore the months and days; if it asks for age at next birthday, add one.

Legal age thresholds

Ages vary between countries and states and change over time; always check the official rules that apply to you.

Why your age in days is surprising

A person who has just turned 27 has lived nearly 10,000 days, and someone turning 31 has passed 11,000. Milestones such as 10,000 days (about 27 years and 4½ months) and one billion seconds (about 31 years and 8 months) make fun celebrations, and the milestone table works out the exact dates for you, including the day of the week.

How leap years affect the count

Total days include every 29 February between the two dates, so two people with the same age in years can have lived a slightly different number of days. Over a lifetime, leap years add about one day every four years, which is why 10,000 days is a little less than 27.4 calendar years.

Common uses

• Checking eligibility for school, sports age groups or benefits.
• Filling in forms that ask for age on a particular date.
• Planning milestone celebrations.
• Genealogy and family history.
• Calculating a pet’s or child’s age precisely.

Privacy

The calculator runs in your browser; dates of birth are not uploaded or stored.