Age Difference Calculator

Enter two dates of birth to see the exact age difference in years, months and days. For one person's age, use the age calculator.

First person's date of birth

Second person's date of birth

Age difference

e.g. Mar 3, 1988 and Jun 14, 1992 → 4 years, 3 months, 11 days

The difference appears here once both dates are in.

Calculated in your browser. The dates you enter never leave this device.

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How the age difference is calculated

The calculator counts from the earlier date of birth to the later one: full years first, then full months, then the days left over. It's the same method as working out someone's age, so end-of-month dates and leap years are handled the same way.

Example: one person was born on March 3, 1988 and the other on June 14, 1992. The difference is 4 years, 3 months, 11 days, or 1,564 days.

Why the difference in years seems to change

The exact difference is fixed for life. But if you compare whole-year ages, it can look different depending on the time of year: right after the older person's birthday the gap in ages is one year bigger than right after the younger person's.

The “half your age plus seven” rule

When both people are adults, the result also shows this well-known rule of thumb for couples: the youngest acceptable partner age is half your age plus seven, and the oldest is your age minus seven, doubled. It's folklore, not science, and it says nothing about any particular couple.

Frequently asked questions

How do you calculate the age difference between two people?

Count from the earlier date of birth to the later one, the same way you'd count someone's age: full years, then full months, then days. The calculator does it as soon as both dates are in.

Does the age difference change over time?

The exact difference never changes. What changes is how it looks in whole years: between their birthdays, two people born 4 years and 3 months apart are sometimes 4 years apart in age and sometimes 5.

What is the “half your age plus seven” rule?

A pop-culture rule of thumb for the youngest age someone “should” date: half their age plus seven. The oldest, by the same rule, is their age minus seven, doubled. It isn't a scientific or legal standard, and it only makes sense for couples.

Can I compare a parent and a child, or two siblings?

Yes. The calculator works for any two dates of birth, including twins born on different days around midnight.