Calculating age using a date of birth in Excel is simple and useful for many tasks like keeping track of birthdays or ages in a list. Excel has special functions like DATEDIF and YEARFRAC that make finding the exact age easy and accurate, even considering months and days. In this blog, you will learn a step-by-step process to calculate age in Excel using your date of birth data with easy formulas anyone can follow.

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1) Age in completed years — recommended (DATEDIF)

Formula

=DATEDIF(A2, TODAY(), "Y")

What it does
Returns the number of full years between the date in A2 and today.

Example
If A2 = 1990-07-15 and today is 2025-11-13, formula returns 35 (35 full years).

Notes

• DATEDIF is an undocumented but built-in Excel function that works across Excel versions (Windows/Mac/365).
• No extra formatting required — just display as a number.

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2) Age as years, months and days (human-readable)

Formula

=DATEDIF(A2, TODAY(), "Y") & " yrs, " & DATEDIF(A2, TODAY(), "YM") & " mos, " & DATEDIF(A2, TODAY(), "MD") & " days"

What it does
Gives a breakdown like: 35 yrs, 3 mos, 29 days.

Notes

• "Y" = full years, "YM" = remaining months after removing whole years, "MD" = remaining days after removing whole months/years.
• MD sometimes produces surprising results around month boundaries (works for most human-readable needs). If you need exact day arithmetic across month boundaries, consider more advanced handling.

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3) Age in decimal years (e.g., 35.29 years) — using YEARFRAC

Formula

=ROUND(YEARFRAC(A2, TODAY(), 1), 2)

What it does
YEARFRAC returns fractional years between two dates. The third argument is a basis (day count convention). 1 uses actual/actual (good default). ROUND(...,2) rounds to 2 decimal places.

Notes

• Useful for calculations that require fractional ages (actuarial, scientific).
• You can change 2 to the number of decimals you prefer.

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4) Simple year difference (not recommended alone)

Formula

=YEAR(TODAY()) - YEAR(A2)

What it does
Gives a rough year difference but will be wrong if the person hasn’t had their birthday yet this year.

If you must use it, make it accurate:

=YEAR(TODAY()) - YEAR(A2) - (DATE(YEAR(TODAY()), MONTH(A2), DAY(A2)) > TODAY())

This subtracts 1 when the birthday for the current year is still in the future.

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5) Age in months (total months)

Formula

=DATEDIF(A2, TODAY(), "M")

What it does
Returns total full months between DOB and today.

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6) Age in days (total days)

Formula

=TODAY() - A2

What it does
Returns total days (Excel stores dates as serial numbers). Format cell as Number (no date format) to see days.