Quick answer: Subtract the birth year from the current year, then take away one if the birthday has not happened yet this year. For months and days, count whole months from the last birthday, then the remaining days — or use a free age calculator, or =DATEDIF(birth_date, TODAY(), “Y”) in Excel or Google Sheets.
Application forms, exam eligibility rules, visas and insurance quotes often ask for your exact age on a specific date. Here is how to work it out by hand, with a spreadsheet formula, or in one step with the free Age Calculator.
Age in years: the quick method
- Subtract the birth year from the current year.
- If the birthday has not yet happened this year, subtract 1.
Example: someone born on 28 November 2000. On 22 October 2026, 2026 − 2000 = 26, but their birthday in November has not arrived yet, so they are 25.
Exact age in years, months and days
- Years: count the full years up to the most recent birthday (as above).
- Months: count the full months from that birthday up to the same day of the month on or before today’s date.
- Days: count the days that remain from there to today.
Worked example 1
Born 15 August 1995, age on 22 October 2026:
- Last birthday: 15 August 2026 → 31 years.
- 15 August → 15 October 2026 → 2 months.
- 15 October → 22 October → 7 days.
Age: 31 years, 2 months and 7 days (11,391 days in total).
Worked example 2 (when you have to “borrow” days)
Born 28 November 2000, age on 22 October 2026:
- Last birthday: 28 November 2025 → 25 years.
- 28 November 2025 → 28 September 2026 → 10 months (28 October has not arrived yet).
- 28 September → 22 October: 2 days to the end of September (which has 30 days) plus 22 days → 24 days.
Age: 25 years, 10 months and 24 days. The length of the month you borrow from matters, which is why hand calculations so often come out a day or two wrong.
Age in total days, weeks or months
- Total days: count every day between the two dates, including leap days. The Date Difference Calculator does this instantly.
- Total weeks: divide the total days by 7. In example 1, 11,391 days = 1,627 weeks and 2 days.
- Total months: years × 12 + the extra months (31 × 12 + 2 = 374 months in example 1).
How to calculate age in Excel or Google Sheets
Put the date of birth in cell A2, then use DATEDIF, which works in both Excel and Google Sheets:
- Years:
=DATEDIF(A2, TODAY(), "Y") - Months after the last birthday:
=DATEDIF(A2, TODAY(), "YM") - Days after the last full month:
=DATEDIF(A2, TODAY(), "MD") - Total days:
=TODAY() - A2(format the cell as a number)
Replace TODAY() with a cell containing another date to get age on that date. Microsoft notes that the "MD" option can give inaccurate results in some cases, so double-check day counts that matter.
Common mistakes to avoid
- Forgetting whether the birthday has passed — the most common reason for being one year out.
- Assuming every month has 30 days — it causes off-by-one errors in the days part.
- Mixing up date formats — 04/05/2010 is 4 May in the UK and many other countries but April 5 in the US.
- Using the wrong “age on” date — exams and schemes often fix a cut-off date, such as 1 January or the closing date for applications. Always calculate age on the date the rules specify.
Calculate age instantly
- Open the free Age Calculator.
- Enter the date of birth.
- Optionally change the “age on” date to a cut-off date.
- Read the age in years, months and days, plus totals in weeks, days and hours.
Frequently asked questions
How do I calculate my age on a specific date?
Use the same steps, but compare the date of birth with the specific date instead of today. In the Age Calculator, change the “Age on” field; in a spreadsheet, replace TODAY() with that date.
How is age calculated for someone born on 29 February?
In non-leap years there is no 29 February, so people usually treat 28 February or 1 March as the birthday. Which one counts legally depends on the country and the purpose, so check the rules that apply to you.
How many days old am I?
Count the days between your date of birth and today, including leap days. The Date Difference Calculator or the Age Calculator shows the total.
Why does my age differ by a day between calculators?
Calculators can differ in how they handle the end of short months and whether they count the start or end date. For official purposes, follow the method the organisation asking specifies.
Need other everyday maths? See how to calculate percentages or browse all free calculators.
Keep reading: related guides
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