What the rule says
The rule sets a lower limit on a partner's age: take your age, halve it and add seven. A 30-year-old gets 22 and a 60-year-old gets 37. Run it backwards (subtract seven, then double) and you get the upper limit, so a 30-year-old's range runs from 22 to 46.
People quote it because it scales with age. A five-year gap looks very different at 19 and 24 than at 45 and 50, and the formula tightens the range for young people and loosens it later in life.
Formula notes
Minimum partner age = your age / 2 + 7Maximum partner age = (your age - 7) x 2
Where the rule came from
The rule is older than most people assume. Frederick Locker-Lampson's Patchwork (1879) says a wife should be half her husband's age with seven years added. Max O'Rell's Her Royal Highness Woman (1901) gives the version most people know: a man should marry a woman half his age, plus seven.
It later turned up in John Fox Jr.'s 1903 novel The Little Shepherd of Kingdom Come, in American newspapers of the 1930s that credited it to Maurice Chevalier, and in The Autobiography of Malcolm X.
What research says about it
A 2001 study by Buunk and colleagues asked people about the youngest and oldest partners they would consider for different kinds of relationships. The half-plus-seven minimum came fairly close to men's answers. It did not describe women's answers well.
Real couples are mostly close in age. In 2017 U.S. Current Population Survey data, about a third of opposite-sex married couples were within two years of each other. So the rule describes the edge of what people find acceptable, not what is typical.
Working out the rule for any age
Use whole-year ages on the same date. If one person is 36 and the other is 27, the minimum for 36 is 25, so 27 passes. If one person is 24 and the other is 18, the minimum for 24 is 19, so 18 falls just short.
The answer can change during a year because ages tick up on different birthdays. Our age gap calculator measures both people on the date you choose and runs the check for you.
- 18: minimum 16, maximum 22
- 21: minimum 17.5, maximum 28
- 25: minimum 19.5, maximum 36
- 35: minimum 24.5, maximum 56
- 45: minimum 29.5, maximum 76
What the rule can't tell you
It's a social rule of thumb with no legal standing. Age-of-consent laws are separate and vary by place, and the formula's minimum for a young teenager can be below them. Never treat the rule as permission.
It also says nothing about whether a relationship is healthy. Gaps matter more when they come with big differences in money, life stage or power, and a formula can't measure those.
Frequently asked questions
How do you calculate half your age plus seven?
Divide your age by two, then add seven. At 28 that's 14 + 7 = 21, so the rule's youngest partner for a 28-year-old is 21.
What is the maximum age by the half-plus-seven rule?
Subtract seven from your age and double the result. At 28 that's (28 - 7) x 2 = 42.
Who came up with half your age plus seven?
It appears in Frederick Locker-Lampson's Patchwork (1879) and in Max O'Rell's Her Royal Highness Woman (1901), which uses the wording most people quote today.
Is the half-plus-seven rule a law?
No. It has no legal meaning, and age-of-consent laws are completely separate.
Does the rule work the same for men and women?
Research from 2001 found it roughly matched the minimum ages men said they'd accept, but not the ages women said they'd accept.
References
These sources support the method or guidance used for Age Difference Calculator. Verify time-sensitive rules at the source.
Try the calculator
Open Age Difference Calculator, enter your scenario, and compare its supporting rows with this guide's method and checks.