How to Calculate Age with Date of Birth

Whether you're filling in an official form, checking exam eligibility, or just curious, calculating age from a date of birth comes down to one idea: count the completed years, then the leftover months and days. Here are three ways to do it — from fully manual to fully automatic.

Method 1: By hand (the borrowing method)

Write both dates as day / month / year and subtract column by column, starting with days. When a subtraction goes negative, borrow from the next column — exactly like long subtraction in arithmetic.

STEP 01Days: subtract birth day from current day. If negative, add the number of days in the previous month and carry −1 to the months.

STEP 02Months: subtract birth month from current month (minus any carry). If negative, add 12 and carry −1 to the years.

STEP 03Years: subtract birth year from current year (minus any carry). Done.

Worked example

Date of birth: 14 November 1992 · Today: 6 July 2026

Column	Working	Result
Days	6 − 14 = −8 → borrow June's 30 days: 36 − 14	22 days
Months	(7 − 1) − 11 = −5 → borrow 12: 7	7 months
Years	(2026 − 1) − 1992	33 years

Age: 33 years, 7 months, 22 days.

Quick check trick: Has the birthday happened yet this year? If yes, age = current year − birth year. If no, subtract one more. 14 November hasn't arrived by 6 July, so 2026 − 1992 − 1 = 33 ✓

Where hand calculation goes wrong

Borrowing the wrong month length. You borrow from the month before the current one (June's 30 days in the example above, not November's 30 or July's 31).
Forgetting February. When the previous month is February, borrow 28 days — or 29 in a leap year. The rules are in our Leap Year Guide.
Off-by-one on the birthday itself. On your birthday, you've completed the year — the new age applies from that day.

Method 2: In Excel or Google Sheets

The DATEDIF function does the whole calculation in one cell. With the date of birth in A1:

Years only:            =DATEDIF(A1, TODAY(), "Y")
Years, months, days:   =DATEDIF(A1,TODAY(),"Y") & " y, " &
                        DATEDIF(A1,TODAY(),"YM") & " m, " &
                        DATEDIF(A1,TODAY(),"MD") & " d"
Total days alive:      =TODAY() - A1

The unit codes: "Y" = complete years, "YM" = months after subtracting the years, "MD" = days after subtracting years and months. Swap TODAY() for any cell containing a target date to get age at that date.

Note: DATEDIF's "MD" unit has documented quirks around end-of-month dates in Excel. For anything critical, verify with a calendar-based tool.

Method 3: Online (the 10-second way)

An online age calculator applies the same borrowing method — with every leap year and month length handled — and adds the extras that are tedious by hand: total weeks, days, hours, minutes, and a countdown to the next birthday.

Open the myagecalc.net age calculator.
Enter the date of birth.
Optionally set an "age at" date (it defaults to today).
Click Calculate — the full breakdown appears instantly.

Everything runs in your browser, so the date of birth is never sent anywhere.

Which method should you use?

Situation	Best method
One-off, no device handy	By hand (borrowing method)
A whole column of birth dates	Spreadsheet with DATEDIF
Exact age with all units, fast	Online calculator
Legal/official cutoff dates	Online calculator with a custom "age at" date

Frequently asked questions

What's the formula for calculating age?

Age = current date − date of birth, computed column-wise: subtract days (borrowing from the previous month if negative), then months (borrowing 12 if negative), then years. The result is expressed as completed years, months, and days.

How do I calculate age in years only?

Subtract the birth year from the current year, then subtract 1 if the birthday hasn't occurred yet this year. That's it.

Why is my day-count age different from my calendar age?

Dividing total days by 365 ignores leap days, so it drifts by about a day for every four years lived. Calendar comparison (the borrowing method) is the accurate approach — see our guide on how age is calculated.

How do I calculate someone's age at a past date?

Use the same method but replace "today" with the target date — or set the "Age at Date" field in our calculator to that date.

Let the calculator do the borrowing

Exact age in years, months, days, hours, and minutes — from one date input.

Calculate Age Now →

Method 1: By hand (the borrowing method)

Worked example

Where hand calculation goes wrong

Method 2: In Excel or Google Sheets

Method 3: Online (the 10-second way)

Which method should you use?

Frequently asked questions

Let the calculator do the borrowing

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