Age Difference and Age Gap Calculator
Enter two birthdays to see the exact age gap between two people in years, months and days, and who is older. Names are optional.
The age gap appears here.
Enter two birthdays and choose Find the age difference. Names are optional.
Only know the birth years?
How the age gap is calculated
We count on the real calendar from the earlier birthday to the later one: whole years first, then whole months, then the days left over. Month lengths and leap years are handled, so the answer is exact rather than an average.
The totals in months, weeks, days and hours are the same gap in other units. To see each person's own age, use the Age Calculator. For a playful match score, try the Birthday Compatibility Calculator, or see how many people share your birthday.
Worked example
Person 1 was born March 21, 1996 and Person 2 on July 4, 1999. From March 21, 1996 to March 21, 1999 is 3 years; to June 21, 1999 is 3 more months; to July 4 is 13 days. The age difference is 3 years, 3 months and 13 days, or 1,200 days.
How to find an age difference by hand
- Write both birth dates and start from the earlier one.
- Count the full years until the anniversary of that date just before the later birthday.
- Count the full months from there.
- Count the days left until the later birthday. Years, months and days together are the age gap.
What the results show
- Years, months and days. The exact gap, counted on the calendar from the earlier birthday.
- Months, weeks, days and hours. The same gap as one number. In days it never changes.
- Ages today. How old each person is now, so you can see the gap in everyday terms.
- Twice as old. The date the older person was exactly twice the younger one's age.
- Birth years only. If you do not know the full dates, the year check gives the two possible gaps.
The gap stays, the ratio shrinks
Two people are always the same number of days apart. What changes is how big that gap feels. A 10-year gap is huge between a 20-year-old and a 10-year-old, and hardly noticeable at 90 and 80.
| Ages | Gap | Older is |
|---|---|---|
| 20 and 10 | 10 years | 2 times as old |
| 30 and 20 | 10 years | 1.5 times as old |
| 40 and 30 | 10 years | 1.33 times as old |
| 60 and 50 | 10 years | 1.2 times as old |
| 90 and 80 | 10 years | 1.13 times as old |
There is one day when the older person is exactly twice as old: the day the younger one is as old as the gap. In the example above, that was Wednesday, October 16, 2002, when Person 2 had lived 1,200 days and Person 1 had lived 2,400.
Finding the gap from birth years
Subtracting the birth years gives the largest whole-year gap. For part of each year, between the two birthdays, the gap in whole years is one less. People born in 1990 and 1995 are 5 years apart from the second birthday of the year until the first one comes round again, and 4 years apart in between.
With only ages to go on, the same applies: two people aged 30 and 25 are somewhere between 4 years and a day and 5 years and 364 days apart. Full dates of birth give the exact answer.
Couples, siblings, parents and friends
The calculator works for any two people. Couples, dating or married, can see their exact age gap and the day one was twice the other's age. Compare siblings to see who is older by how many days, find how old a parent was when a child was born, or settle which friend is the oldest in the group. For the age a parent will be on a child's birthday, or each person's exact age, use the Age Calculator with the "Age on" date.
Sharing a birthday with someone? The Birthday Twin Finder shows how many others do too, and How Rare Is My Birthday shows where your date ranks.
Age Difference Calculator questions
How do you calculate the age difference between two people?
Count from the earlier birth date to the later one: first the full years, then the full months, then the days left over. The result is the same no matter whose birthday you enter first.
Is the age difference the same every year?
Yes. Two people are always the same distance apart, so the gap in days never changes. What changes is the gap in whole years for part of the year, between the two birthdays.
What is an acceptable age difference for a couple?
There is no official rule: it is up to the two adults. The best-known rough guide is the half your age plus seven joke rule, which says a 40-year-old would date people 27 and older.
What is the half your age plus seven rule?
A rule of thumb for adults dating: the youngest age someone should date is half their age plus seven. By that rule a 30-year-old would date people 22 and older. It is a joke rule, not advice, and the tool only shows it for adults aged 22 and over.
Is an age gap calculator the same as an age difference calculator?
Yes. Both find the time between two birth dates. This one shows the age gap in years, months and days, and in total weeks, days and hours.
Can I use it for siblings or parents?
Yes. The calculator works for any two people: partners, siblings, a parent and child, or friends.
How many years apart are people born in 1990 and 1995?
4 or 5 years. They are 5 years apart once both have had their birthday in a year, and 4 years apart in the part of the year between the two birthdays. Enter full dates for the exact gap.
When was one person twice the other's age?
On the day the younger person was as old as the gap between you. If you are 3 years older than your sister, you were twice her age when she turned 3. The tool gives the exact date.
Does the age gap get smaller as we get older?
The gap stays the same, but it matters less. At 20 and 10 one person is twice as old; at 90 and 80 they are only about 1.1 times as old.
What if we were born on the same day?
Then the age difference is zero, and the tool says so. Twins born either side of midnight can have different birthdays and a gap of one day.
Are the birth dates saved?
No. The calculation runs in your browser and nothing you enter is sent to or stored on our server.
Related tools
Age Calculator
Your exact age in years, months, days and seconds.
Birthday Compatibility Calculator
A match score for two birthdays.
Birthday Twin Finder
How many people share your birthday, and the odds of meeting one.
Published October 4, 2026. Last updated October 4, 2026. Uses the Gregorian calendar and your device's time zone.