How to use this age calculator
- Age: enter a date of birth. “Age on” starts at today, but you can pick any date, for example to check an age on the day of an exam or an application deadline. You’ll see the exact age, the totals in months, weeks, days, hours and minutes, the day of the week of the birth, and the next birthday.
- Baby age: enter the baby’s birth date to see the age in weeks and days, the way baby ages are usually given, plus months and days.
- Birth date from age: enter an age and the date it applies to, and the calculator counts back to the birth date and shows the working.
Everything is calculated in your browser. Nothing is saved or sent anywhere.
How to calculate your exact age
An exact age is counted in three steps: whole years, then whole months, then the leftover days.
- Count the birthdays that have passed: that’s the age in years.
- From the last birthday, count whole months, each one ending on the same day of the month.
- Count the days from the last of those months to the date you want.
Worked example: someone born on 15 May 2000, on 22 October 2026. Their last birthday was 15 May 2026, so they are 26 years old. From 15 May to 15 October is 5 months, and from 15 October to 22 October is 7 days. Their age is 26 years, 5 months and 7 days, which is 9,656 days in total. They were born on a Monday, and their next birthday is Saturday, 15 May 2027, when they turn 27.
Why months make age tricky
Years and days are easy, but months come in four lengths: 28, 29, 30 and 31 days. This calculator counts a whole month from one day of the month to the same day of the next month. If that day doesn’t exist, it uses the last day of the month. So:
- 28 February to 28 March is 1 month, so 28 February to 31 March is 1 month and 3 days.
- 31 January to 28 February (or 29 February in a leap year) is 1 month, because February has no 31st.
The Date Calculator on this site uses exactly the same rule, so the two always agree. Other tools that convert days to months using an average month length of about 30.4 days can be a day or two different, which is why your age in months and days can vary slightly between websites.
Leap-day (29 February) birthdays
Someone born on 29 February only has a real birthday every four years or so. In the years in between, this calculator counts the birthday on 28 February, so a person born on 29 February 2004 turns 1 on 28 February 2005. Some places, and some laws, use 1 March instead. If that matters for something official, check the local rules. The calculator shows a note whenever a 29 February birthday is involved.
Different ways of counting age around the world
The method used here, where everyone starts at 0 and gains a year on each birthday, is the most widely used today. It hasn’t always been universal, though. Some traditional systems, historically used in parts of East Asia, count a newborn as one year old and add a year at the new year rather than on the birthday, so the same person can have a different age depending on the system. If you need an age for an official document, use the method that document expects.
How to work out a baby’s age in weeks and months
For babies and young children, ages are usually given in weeks and then months, because a few weeks makes a big difference early on. To find the age in weeks, count the days since the birth and divide by 7: the whole number is the weeks and the remainder is the extra days. A baby born on 1 August 2026 is 82 days old on 22 October 2026, which is 11 weeks and 5 days, or 2 months and 21 days using the same-day-of-the-month rule. For children under two, the calculator also gives the age simply as a number of months, such as “2 months old”.
Frequently asked questions
How do I calculate my exact age?
Count the whole years since your birthday, then the whole months since your last birthday, then the days since the same day of the month. Someone born on 15 May 2000 is 26 years, 5 months and 7 days old on 22 October 2026.
How are months counted when they have different lengths?
A whole month is counted from one day of the month to the same day of the next month. If that day doesn’t exist, the last day of the month is used. So 28 February to 31 March is 1 month and 3 days, because 28 February to 28 March is one month.
When do people born on 29 February celebrate their birthday?
In leap years, on 29 February. In other years this calculator counts the birthday on 28 February, which is common, but some places and some legal systems use 1 March instead.
How old is my baby in weeks?
Count the days since the birth and divide by 7. The whole number is the weeks and the remainder is the extra days. A baby born on 1 August 2026 is 82 days old on 22 October 2026, which is 11 weeks and 5 days, or 2 months and 21 days.
Can I find a date of birth from an age?
Yes. Use the “Birth date from age” tab: enter the age in years (and optionally months and days) and the date it applies to. The calculator counts back and checks the answer, so 30 years on 22 October 2026 gives a birth date of 22 October 1996.
Does this calculator save my date of birth?
No. Everything is worked out in your browser and nothing is saved or sent anywhere. Refreshing the page clears it.