In Excel: put the birth date in A2 and use =DATEDIF(A2,TODAY(),"Y") to return the completed age in whole years.
On this page7
Put the date of birth in A2.
In B2 enter =DATEDIF(A2,TODAY(),"Y").
Format the result cell as a plain number, not a date.
Use "M" for months or "D" for days if you need finer detail.
What this does
DATEDIF measures the gap between a start date and an end date in the unit you ask for. With the birth date as the start, TODAY() as the end and "Y" as the unit, it returns the number of full years lived — the person's current age. Swap the unit to "M" for whole months or "D" for total days. DATEDIF is hidden from the function list but works in every Excel version and in Google Sheets. Most people learn this as a sequence of clicks and forget it by next week; learning it as a pattern instead is what lets you apply it to the next, slightly different version of the problem without starting from scratch. That is the difference this page is trying to make. Treat “excel age formula from dob” as a small repeatable workflow rather than a one-off click you hope to remember next time. Use a small test block before the live file, so any surprise in the affected formula shows up while it is still harmless. When a formula is involved, keep the inputs labelled beside it, reference cells instead of typing values, and apply number formatting only after the result checks out. That turns a calculation you can defend to a CFO or an auditor into a method you can reuse, explain, and defend when the workbook leaves your screen.
A worked example
A2 holds the birth date 1990-06-15. In B2 type =DATEDIF(A2,TODAY(),"Y"). With today around 2026 the result is 35, because the person has completed 35 birthdays. You reach for DATEDIF whenever a report needs a live age from a birth date — staff records, customer profiles, eligibility checks — that recalculates as time passes. Check the referenced cells, argument order and result type in your workbook. Start with the worked example before changing an input, then compare the changed result with the calculation you expected. An error value or a result of a different type is a reason to inspect the inputs and arguments.
In Google Sheets
Google Sheets support for this task has not been verified. Check the function, arguments and workflow in the target product before transferring the example. Matching formula notation does not establish identical behaviour. Nothing on this page is behind a login or a download: the exact answer is at the top, and the detail below it is there for when you need it. That is the whole promise here — the answer first, and just enough context to make it stick. For “excel age formula from dob”, keep the input cells and the result visible while you check the formula in Excel. Follow the worked example and change one input at a time. The steps explain the workbook calculation; this page does not run a live calculator for that task.
Common mistakes
- Formatting the result as a date, so 35 shows as a date instead of a number.
- Using "Y" when you actually wanted months or days.
- Putting the dates in the wrong order — start must be earlier than end or
DATEDIFerrors. - Hard-coding today's date instead of
TODAY(), so the age never updates.
Frequently asked questions
Why is DATEDIF not in the function list?
It is a Lotus 1-2-3 compatibility function, so Excel gives it no entry and no autocomplete — type it in full. Microsoft does document it, and advises against the "md" unit in particular.
How do I get age in months or days?
Replace "Y" with "M" for whole months or "D" for total days.
Is there an alternative?
Yes. =YEARFRAC(A2,TODAY()) gives a decimal age you can round down with INT.
Other ways people ask this
This is also commonly searched as “excel formula age from dob” and “excel formula for age from dob”. They describe the identical operation, so you are in the right place no matter how you phrased it.
Why do people search for this in so many different ways?
Because the same task has many names. “excel formula age from dob”, “excel formula for age from dob” all point at the one operation explained on this page, which is why they all lead here.