Age gap
How the age difference calculator works out an age gap
By Toheed MehmoodReviewed How we check facts
In short
Count from the earlier date of birth to the later one, in whole years, then months, then days. Born 12 April 1990 and 3 September 1994, two people are 4 years, 4 months and 22 days apart, or 1,605 days. The gap never changes, even though both ages go up each year.
- Example gap
- 4 years, 4 months, 22 days
- Same gap in days
- 1,605
- Rule of thumb
- Half your age + 7
How to use the age difference calculator
- Enter the first person's date of birth.
- Enter the second person's date of birth. The order does not matter.
- Read the gap in years, months and days, then the same gap in days, weeks and months, and who is older.
Why subtracting ages can give the wrong gap
Subtracting current ages (36 minus 32 = 4) only gives whole years, and it changes during the months between the two birthdays. Comparing the dates of birth gives the exact gap, which stays the same for life.
The “half your age plus seven” rule
A popular rule of thumb says the youngest person you should date is half your age plus seven, rounded up to a whole year. Turned around, the oldest is your age minus seven, doubled. At 30 that gives a range of 22 to 46.
| Your age | Youngest | Oldest |
|---|---|---|
| 20 | 17 | 26 |
| 25 | 20 | 36 |
| 30 | 22 | 46 |
| 40 | 27 | 66 |
| 50 | 32 | 86 |
The rule is often credited to the French author Max O'Rell, who wrote in 1901 that a bride should be half the groom's age plus seven. It is a joke-adjacent guideline, not research, and it says nothing about whether a relationship is healthy.
Other reasons to check an age gap
- The age gap between siblings, for school years and shared activities.
- The age difference between parents and children.
- Comparing which generation two people belong to: see What Generation Am I?.
Common questions
How do I calculate the age difference between two people?
Count from the earlier birth date to the later one in years, months and days. The calculator does this exactly, including leap years.
Does the age gap change over time?
No. The difference between two birth dates is fixed. Only the ratio between the ages changes.
What is the half your age plus seven rule?
A rule of thumb for dating: the youngest acceptable partner is half your age plus seven, and the oldest is twice your age minus seven.
Can I compare twins or people born the same day?
Yes. The calculator shows a difference of zero when both dates are the same.
Can I see the age gap in days or months?
Yes. Along with years, months and days, the calculator shows the gap as total days, weeks and months.
Who counts as older if we share a birth year?
The person with the earlier date of birth. The calculator names who is older and by how much, even when the gap is only days.
Sources
- Half your age plus seven · Dictionary.com
- Gregorian calendar · Encyclopaedia Britannica
- What is a leap year? · Royal Museums Greenwich