Age Calculator

Work out how old you are in years, months and days, and how many days are left until your birthday.

Age in years

15 July 1990 · 6 October 2026

Plus months

Plus days

Age in months

434

Age in weeks

1,890

Age in days

13,232

Days until the next birthday

282

Next birthday

15 July 2027

Please note: The result is an estimate and has been rounded. Actual costs and values may differ, and no rights can be derived from this calculation.

How this number is calculated

The blocks use your input. Change a value above and they update with it.

Step 1 · Whole months

year ofAge on6 October 2026 − year ofDate of birth15 July 1990 × Months per year12 + month ofAge on6 October 2026 − month ofDate of birth15 July 1990 − (becauseday ofAge on6 October 2026 less than day ofDate of birth15 July 1990 ) 1 =Whole months434

Step 2 · Age in years

Whole years36 =Age in years36

Step 3 · Plus months

Whole months434 mod Months per year12 =Plus months2

Step 4 · Last whole month ended on

(becauseday ofAge on6 October 2026 less than day ofDate of birth15 July 1990 ) smallest ofFirst day of the month1 October 2026 − 1 − day ofFirst day of the month1 October 2026 − 1 + day ofDate of birth15 July 1990 First day of the month1 October 2026 =Last whole month ended on15 September 2026

Step 5 · Plus days

Age on6 October 2026 − Last whole month ended on15 September 2026 =Plus days21

Step 6 · Age in days

Days since birth13,232 =Age in days13,232

Step 7 · Last birthday

date fromyear ofDate of birth15 July 1990 + Whole years36 month ofDate of birth15 July 1990 1 + day ofDate of birth15 July 1990 − 1 =Last birthday15 July 2026

Step 8 · Days until the next birthday

Days until the birthday282 =Days until the next birthday282

Step 9 · Next birthday

Age on6 October 2026 + Days until the birthday282 =Next birthday15 July 2027

How the calculation works

Enter a date of birth and the date you want to know the age on. You see the age in years, months and days, also as a total number of months, weeks and days, and how many days are left until the next birthday.

You turn a year older on your birthday. The calculator first counts the whole months since birth: a month is complete when the same day of the month comes round again. Twelve whole months make a year; the months and days left over are added. If you were born on 29 February, your birthday counts on 1 March in years without 29 February. The total number of days is the difference between the two dates.

Formula

Months = (year − birth year) × 12 + (month − birth month), minus 1 if the day of the birth month has not been reached yet. Age = months ÷ 12, rounded down. Days = date − date of birth. Weeks = days ÷ 7, rounded down.

Assumptions

You turn a year older on the day of your birthday itself.
Born on 29 February? In a year without 29 February your birthday counts on 1 March.
A month is complete on the same day of the month. If that day does not exist, such as 31 April, the 1st of the following month counts.
If today is your birthday, there are 0 days until your birthday.
Only whole days count: the time of birth and time zones are left out.

Example calculations

The button fills in the calculator above, so you can carry on from there.

Age on your first day at work

Age in years
22

Date of birth 12 March 2004 · Age on 1 September 2026

Born on 12 March 2004, first day at work on 1 September 2026.
Age of a baby

Age in years
0

Date of birth 20 March 2026 · Age on 4 October 2026

Born on 20 March 2026: 6 months and 14 days old on 4 October.
Born on 29 February

Age in years
19

Date of birth 29 February 2008 · Age on 1 March 2027

Born on 29 February 2008: in 2027 the birthday falls on 1 March.

Frequently asked questions

How do I calculate my age?

Subtract your year of birth from the current year. If you have not had your birthday yet this year, subtract 1. Born on 15 July 1990? On 4 October 2026 you are 2026 − 1990 = 36, because your birthday has already passed.

How old am I in days?

That is the number of days from your date of birth to today, including every leap day. Someone born on 15 July 1990 is exactly 13,230 days old on 4 October 2026. Enter your own date of birth and the calculator works it out.

When is my birthday if I was born on 29 February?

In a leap year simply on 29 February. In other years this calculator uses 1 March, because only then has the whole of 28 February passed. Official rules can differ: some countries and organisations use 28 February instead.

How many days until my birthday?

Enter your date of birth and set ‘Age on’ to today's date. The calculator shows how many days are left and on which date your next birthday falls. If today is your birthday, it shows 0.

How do I work out a baby's age in months?

Count the whole months since birth. A baby born on 20 March is 1 month old on 20 April and 6 months and 14 days old on 4 October. The calculator also shows the total number of weeks, which is handy in the first year.

Can I calculate my age on another date?

Yes. Enter any date under ‘Age on’, in the past or in the future. That way you can see how old you were on your wedding day, or how old you will be on your first day at a new job.

Sources and checks

Sources

Leap Years | U.S. Naval Observatory, Astronomical Applications Departmentaa.usno.navy.mil · accessed 5 October 2026

How we check it

This calculator has 21 fixed checks: 17 calculations with a result that is fixed in advance, and 4 cases of invalid input that must be rejected. They all run automatically every time we publish; if one fails, the calculator does not go live.

See the calculations

Date of birth 15 July 1990 · Age on 4 October 2026 → Age in years 36
Date of birth 12 March 2004 · Age on 1 September 2026 → Age in years 22
Date of birth 20 March 2026 · Age on 4 October 2026 → Age in years 0
Date of birth 29 February 2008 · Age on 1 March 2027 → Age in years 19
Date of birth 29 February 2000 · Age on 28 February 2027 → Age in years 26
Date of birth 29 February 2000 · Age on 29 February 2028 → Age in years 28
Date of birth 29 February 2000 · Age on 28 February 2028 → Age in years 27
Date of birth 4 October 1990 · Age on 4 October 2026 → Age in years 36
Date of birth 5 October 1990 · Age on 4 October 2026 → Age in years 35
Date of birth 4 October 2026 · Age on 4 October 2026 → Age in years 0

Changes

5 October 2026: Sources added and content reviewed.
4 October 2026: First version.

Last reviewed: 5 October 2026 · How we build and check our calculators