In Excel: put the birth date in A2 and use =DATEDIF(A2,TODAY(),"Y") to return the completed age in whole years.
35 years · 6 months · 17 days
Next birthday in 165 days · 12,984 days lived
Need it as an auditable file?
Ships inside the linked template — formula-driven, unlocked, audit-ready.
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. The same idea underpins a lot of everyday Excel work, so the few minutes spent getting it right here pay back across every sheet you build afterwards. Treat it as a pattern, not a one-off, and it stops being something you look up and starts being something you reach for. The difference between a quick fix and a sheet you can trust is the extra minute you spend validating “calculate age using date of birth in excel”. Start on a copy or a tiny sample, keep the affected cells visible, and compare the result with the tool above before you touch the real workbook. 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. The point is a calculation you can defend to a CFO or an auditor, but the practical win is that someone else can open the file and understand what happened without asking you.
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. If there is any chance you will reuse this, drop it into a small template tab right now: a labelled input area on the left and the formula beside it, checked once against the tool above. Next time the same question comes up, the answer is a single paste away instead of a rebuild from memory.
In Google Sheets
Google Sheets handles this almost identically to Excel. The formula syntax above is the same, and the menu lives under a slightly different label rather than a ribbon tab. Use the platform toggle at the top of the page to switch every keyboard shortcut between Windows and Mac, and expect at most cosmetic differences in naming. Nothing on this page is behind a login: the tool runs entirely in your browser, the formula is shown in full with one-click copy, and the steps work the same on Windows and Mac. That is the whole promise here — the exact answer, a way to prove it on your own numbers, and just enough context to make it stick. The short version of “calculate age using date of birth in excel”: the answer is at the top of this page, the tool proves it on your own numbers, and the sections above explain why it holds so the next variation does not stump you. Excel rewards people who reference cells instead of typing values and who keep inputs separate from formulas, because that is what makes a result you can audit months later. Build it once, deliberately, with the live tool as a check, and you convert a one-off lookup into a reusable skill — which is the whole point of learning the why and not just the what.
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 undocumented but still works when you type it manually.
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
People reach this page typing “how to calculate age in excel using date of birth”, “how to calculate age in excel with date of birth” and “date of birth formula to calculate age in excel”, among other phrasings; whichever wording you used, the fix above is the one you want.
Why do people search for this in so many different ways?
Because the same task has many names. “how to calculate age in excel using date of birth”, “how to calculate age in excel with date of birth”, “date of birth formula to calculate age in excel” all point at the one operation explained on this page, which is why they all lead here.