Excel Age Formula from Dob

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. One habit worth forming early: name the cells that hold your inputs, so the formula reads in plain language instead of a string of cell addresses. A reviewer — or you in three months — can then follow the logic without decoding what B7 and D2 were supposed to mean, which is most of what makes a sheet maintainable.

In Google Sheets

If you are in Google Sheets rather than Excel, the good news is that the formula shown here is identical and the workflow barely changes — menus sit across the top instead of in a ribbon, and a few function names differ slightly, but anything you build here moves across with little or no rework. 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. Treat “excel age formula from dob” as a small building block rather than a chore. Once the inputs sit in their own cells and the formula reads from them, the same setup answers a dozen related questions with a tweak, and Excel keeps every dependent figure current as the data changes. The tool above is there so you can rehearse and verify before committing anything to a real workbook; the steps and worked example are there so the logic sticks. Get it right once and it stops costing you time — it starts saving it, every time the question comes back around.

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 DATEDIF errors.
• Hard-coding today's date instead of TODAY(), so the age never updates.

Frequently asked questions