Enter a date of birth in the age calculator to get the exact age in years, months and days, the total days lived and the next birthday. You can also pick any “age on” date.
Calculate your ageHow to calculate age in years from date of birth
- Subtract the birth year from this year. Born in 1990, and it’s 2026: 2026 − 1990 = 36.
- Check whether the birthday has come yet this year. If it hasn’t, take 1 off. Someone born in December 1990 is still 35 in October 2026.
That’s all an age in years is: the number of birthdays that have passed.
| Date of birth | On 9 October 2026 | Birthday passed? | Age |
|---|---|---|---|
| 14 March 1990 | 2026 − 1990 = 36 | Yes | 36 |
| 25 December 2001 | 2026 − 2001 = 25 | No | 24 |
| 9 October 2008 | 2026 − 2008 = 18 | Yes, today | 18 |
| 10 October 2008 | 2026 − 2008 = 18 | No, tomorrow | 17 |
Age in years, months and days
Count forward from the last birthday:
- Find the last birthday: for someone born on 14 March 1990, on 9 October 2026 that’s 14 March 2026. Age 36.
- Count whole months from it: 14 March to 14 September is 6 months.
- Count the days left: 14 September to 9 October is 25 days.
Born 14 March 1990, on 9 October 2026: 36 years, 6 months and 25 days
Counting forward like this avoids most mistakes, because you never have to remember how long each month is until the very last step.
The borrowing method, written as a subtraction
Schools often teach this as a subtraction of day, month and year, borrowing when a column would go negative. For someone born on 25 December 2001, on 9 October 2026:
| Year | Month | Day | |
|---|---|---|---|
| Today | 2026 | 10 | 9 |
| Date of birth | 2001 | 12 | 25 |
| Borrow a month: 9 + 30 days of September | 2026 | 9 | 39 |
| Borrow a year: 9 + 12 months | 2025 | 21 | 39 |
| Subtract | 24 | 9 | 14 |
The answer is 24 years, 9 months and 14 days. When you borrow a month, add the number of days in the month before the current one, here September’s 30. Using a flat 30 every time gives answers a day or two off.
Age in days, weeks or months
For a total, count every day between the two dates. Doing it by hand means adding 365 for each year, 1 for each 29 February in between, and the days in the part-years. A calculator or spreadsheet is far quicker:
| Date of birth | Days old on 9 October 2026 | Weeks | Months |
|---|---|---|---|
| 14 March 1990 | 13,358 | 1,908 weeks and 2 days | 438 |
| 25 December 2001 | 9,054 | 1,293 weeks and 3 days | 297 |
A total in months is the years × 12 plus the extra months: 36 × 12 + 6 = 438. The date calculator counts the days between any two dates.
Age on a cut-off date
Exam notices, school admissions and sports leagues often ask for your age “as on” a fixed date rather than today. Do exactly the same sum with that date in place of today’s.
Born 20 August 2003, age as on 1 August 2026: 22 years, 11 months and 12 days
The birthday in August 2026 hasn’t come by the 1st, so the person is still 22. Many notices also print the range of birth dates that are allowed. If yours does, compare your date of birth with that range directly; it settles any doubt about a birthday that falls on the cut-off day. In the age calculator, set the “age on” date to the cut-off.
Days until the next birthday, and the age gap between two people
Next birthday. Take this year’s birthday, or next year’s if it has passed, and count the days from today. On 9 October 2026:
| Date of birth | Next birthday | Days to go | Turns |
|---|---|---|---|
| 14 March 1990 | Sunday, 14 March 2027 | 156 | 37 |
| 25 December 2001 | Friday, 25 December 2026 | 77 | 25 |
Age gap. The difference between two people’s ages is the time between their two dates of birth, and it never changes. Count it the same way as an age, from the older person’s birthday to the younger one’s:
14 March 1990 to 25 December 2001 = 11 years, 9 months and 11 days
Subtracting the two ages in years alone (36 − 24 = 12) gives the wrong answer for most of the year, because the two birthdays fall at different times. The date calculator gives the exact gap in days.
How to calculate age in Excel or Google Sheets
With the date of birth in A2, both Excel and Google Sheets have a DATEDIF function:
| To find | Formula |
|---|---|
| Age in whole years | =DATEDIF(A2,TODAY(),"Y") |
| Months after the last birthday | =DATEDIF(A2,TODAY(),"YM") |
| Days after the last month | =TODAY()-EDATE(A2,DATEDIF(A2,TODAY(),"M")) |
| Total days | =TODAY()-A2 |
| Total months | =DATEDIF(A2,TODAY(),"M") |
| Age on a cut-off date | =DATEDIF(A2,DATE(2026,8,1),"Y") |
DATEDIF also has an “MD” unit for the leftover days, but Microsoft recommends not using it because it can return a negative number, a zero or a wrong result. The EDATE formula above avoids it. Format the “total days” cell as a number, not a date, or Excel shows it as a date in 1936.
Born on 29 February
In years without a 29 February, when does a leap-day baby turn a year older? It depends on the rule being used:
- 28 February. Counting by months, a birthday that doesn’t exist falls on the last day of the month. The age calculator and Excel’s EDATE both work this way.
- 1 March. Some laws choose this instead. Scotland’s Age of Legal Capacity (Scotland) Act 1991 says that a person born on 29 February has their birthday on 1 March in a non-leap year.
For anything legal, such as a driving licence or a contract, check the rule for your country. For everyday purposes, both dates are used.
Common mistakes
- Only subtracting the years. 2026 − 2001 is 25, but the person isn’t 25 until their December birthday.
- Mixing up date formats. 03/04/2001 is 3 April in most of the world and 4 March in the US. Write the month as a word when it matters.
- Dividing days by 365. 13,358 ÷ 365 = 36.6, which is close, but leap years make this drift by a day every four years. It can get the age wrong in the days around a birthday.
- Counting both the first and the last day. The number of days between two dates doesn’t include the start day. Some forms want an inclusive count, which is one more; check which the form means.
- Mixing up the time zone. Someone born late in the evening in one country may have a different birth date in another. Always use the date on the birth certificate.
- Borrowing 30 days for every month. Use the real length of the month before.
Sources
- Microsoft Support: DATEDIF function. Units Y, M, D, MD, YM and YD; known limitations of “MD”
- Google Docs Editors Help: DATEDIF. DATEDIF(start_date, end_date, unit) in Google Sheets
- legislation.gov.uk: Age of Legal Capacity (Scotland) Act 1991, section 6. A 29 February birthday is taken to be 1 March in a non-leap year