The gap in other units
- Months
- –
- Weeks
- –
- Days
- –
- Hours
- –
Age Difference Calculator
Enter two dates of birth to see the exact age gap between them, who is older, and how the gap compares over time.
Age difference
–years
–months
–days
Enter two dates of birth to see the age gap.
Then and now
- First person today
- –
- Second person today
- –
- Older person was twice as old
- –
- Age ratio today
- –
How the age gap is calculated
The calculator finds the earlier of the two dates of birth and counts forward to the later one, the same way you count your own age: whole years first, then whole months, then the days left over. It uses the real length of every month, so a gap that spans February is never off by a day or two, and leap years are handled automatically.
You can enter the dates in either order. The result tells you who is older, by how much, and what the gap is in months, weeks, days and hours.
A worked example
Say the first person was born on 12 March 1990 and the second on 30 November 1993.
- From 12 March 1990 to 12 March 1993 is 3 full years.
- From 12 March to 12 November 1993 is 8 full months.
- From 12 November to 30 November is 18 days.
The first person is older by 3 years, 8 months and 18 days, which is 1,359 days.
The gap stays the same, but it feels smaller
In days, an age gap never changes. In proportion, it shrinks all the time. When the younger person in our example turned one, the older one was more than four times their age. By their thirties, the older one is only about 10% older, and the ratio keeps creeping towards 1.
There’s one neat moment along the way: the day the older person was exactly twice as old as the younger. It happens when the younger person has been alive for exactly the length of the gap. In our example that was 20 August 1997. The calculator works it out for any pair under Then and now.
Common reasons to compare two ages
- Siblings and twins: settle exactly how much older someone is, down to the day.
- Parents and children: the age gap between a parent and a child is the parent’s age on the day the child was born.
- Couples: compare ages precisely, or work out whose birthday comes first in the year.
- Family history: compare generations or check dates in old records.
- Team and school groups: check that ages fall within a band.
The “half your age plus seven” rule
Search for age gaps and you’ll soon find the “half your age plus seven” rule: divide the older partner’s age by two and add seven to find the youngest “acceptable” age for a partner. By that rule a 30-year-old’s lower limit is 22. It’s a cultural rule of thumb, not a finding from research, and plenty of people ignore it entirely. We mention it because people often ask, not as advice.
Comparing ages on a particular date
To compare two people’s ages on a specific day, such as a wedding or a historic event, use the main age calculator for each person with the Age on field set to that date. For the number of days between any two dates that aren’t birthdays, use the date difference calculator. The age gap itself is the same on every date.
Last reviewed on by the Ageculator Team. See how we calculate.
Frequently asked questions
How do I work out the age difference between two people?
Take the earlier date of birth and count forward to the later one: first the whole years, then the whole months, then the remaining days. That’s exactly what this calculator does. You can also subtract one person’s age from the other’s, but it’s easy to slip when months and days are involved.
Does the age difference change over time?
No. The gap between two dates of birth is fixed, so the older person is always older by the same number of days. What changes is how big that gap feels: a three-year gap is huge between a 1-year-old and a 4-year-old, but barely noticeable between people aged 60 and 63.
How old was my mum or dad when I was born?
Enter your parent’s date of birth as the first person and your own as the second. The age difference is exactly how old they were on the day you were born.
What if both people were born on the same day?
Then the age difference is zero. Twins are usually born minutes apart, but if they arrive either side of midnight they can have different birthdays and a one-day age gap.
What is the “half your age plus seven” rule?
It’s a popular rule of thumb for relationship age gaps: divide the older partner’s age by two and add seven to get the youngest “acceptable” age. It has no scientific basis, and we include it only because people often ask about it.