Age Difference Calculator: Gap Between Two Birthdays Free

To find the exact age difference between two people, put the older person's date of birth in the first box of the free age calculator and the younger person's date of birth in the "Age on" box. The answer is the gap in years, months and days, plus the total in months, weeks and days. For birthdays of 14 March 1994 and 2 November 1997, the gap is 3 years, 7 months and 19 days, or 1,329 days.

Why this trick works

The age calculator answers one question: how old was someone born on date A, on date B? If date B is the day the second person was born, the answer is exactly how old the first person was at that moment. That's the age difference, and it stays the same for the rest of their lives.

So you don't need a special "age gap" tool. You need the two birthdays in the right order.

Use the age calculator as an age difference calculator

1. Open the free age calculator.
2. In Date of birth, enter the older person's birthday.
3. In Age on, replace today's date with the younger person's birthday.
4. Read the gap in years, months and days at the top.
5. Below it, Total months, Total weeks and Total days give the same gap in single units.

If you put the dates the wrong way round, the calculator says: "The date of birth is after the 'Age on' date. Check the two dates." Swap them and the answer appears.

Ignore the Next birthday tile for this use. It counts from the second date, so it isn't meaningful for an age gap.

Worked examples

Siblings. An elder sister was born on 14 March 1994 and her brother on 2 November 1997.

• Full years: from 14 March 1994 to 14 March 1997 is 3 years.
• Full months: 14 March 1997 to 14 October 1997 is 7 months.
• Days: 14 October to 2 November is 19 days.

The gap is 3 years, 7 months and 19 days: 43 total months, 189 total weeks, 1,329 total days.

A couple. One partner was born on 23 August 1988 and the other on 5 January 1992. The gap is 3 years, 4 months and 13 days, or 1,230 days.

Parent and child. A mother born on 30 May 1961 and a son born on 12 September 1990: she was 29 years, 3 months and 13 days old when he was born. That's 10,697 days.

Age gap as a decimal

Sometimes you want a single number, such as "3.6 years". Take Total days and divide by 365.25 (the average year length once leap years are counted):

• 1,329 ÷ 365.25 = 3.64 years
• 1,230 ÷ 365.25 = 3.37 years

The years-months-days answer is more exact for everyday talk. The decimal is handy for spreadsheets or comparing many pairs.

Getting the gap in days, weeks and weekdays

If you need the gap as a plain count of days, the free date calculator gives the same answer from a different angle. Choose Days between dates, enter the two birthdays as Start date and End date, and you'll see:

• the total days (1,329 for the siblings above),
• Weeks and days (189 weeks, 6 days),
• Years, months, days (3 years, 7 months, 19 days),
• Weekdays (Mon to Fri), which isn't very useful for birthdays but is there if you need it.

The date calculator doesn't mind which date comes first: if the end date is earlier, it shows a negative count. The guide to counting days between two dates covers its other options, such as including the end date.

The gap stays the same, the ratio doesn't

The age difference between two people never changes: the siblings above will always be 3 years, 7 months and 19 days apart. What changes is how big that gap feels. When the brother is 10, his sister is about 36% older than him. When he's 50, she's only about 7% older. That's why a 10-year gap feels huge between a 5-year-old and a 15-year-old, and barely noticeable at 45 and 55.

Month-end birthdays

Months have different lengths, so "1 month" isn't a fixed number of days. The calculator counts calendar months, the way people count birthdays. When a birthday falls on a day a month doesn't have, such as the 31st, it uses the last day of the shorter month.

For example, birthdays of 31 January 1999 and 1 March 1999 are 1 month and 1 day apart: one month takes you to 28 February (February 1999 had no 29th or 31st), then one more day to 1 March. In total days, that's 29.

This rarely matters for age gaps measured in years, but it explains why two tools can disagree by a day or two in the months-and-days part while agreeing on total days.

When an exact age gap is needed

• Family records and trees: the gap between generations, or a parent's age at a child's birth.
• Insurance and pension forms: some policies ask for the age difference between spouses for joint-life cover.
• Adoption rules: some countries set a minimum age gap between adoptive parent and child. Check the official rules where you live.
• Twins and close siblings: a gap of a few hours won't show, since the calculator works in whole days. Twins born either side of midnight show a gap of 1 day.

For an age on a specific date rather than a gap, see how to calculate age from date of birth.

Find your age gap now

Enter the older birthday and set "Age on" to the younger birthday in the free age calculator. It's free, there's nothing to sign up for, and the dates you enter stay on your device.