How It Works
Enter both dates of birth and, if you like, an "as of" date. The calculator subtracts the earlier birthdate from the later one to find the exact age difference between partners.
It works like date subtraction by hand. If the day count goes negative, it borrows the length of the previous month; if the month count goes negative, it borrows 12 months from the year.
What the results show
- Exact gap: years, months and days between the two birthdates, plus the total in calendar days.
- Rule check: whether the younger person meets the half your age plus seven minimum for the older person's age.
- Statistical rarity: the reference band your gap falls into, from under 1 year (about 33% of couples) to 20+ years (under 1%).
- Generations and life stage: each person's generational cohort and a label such as Young Professional or Established Adult.
Ages are taken on the selected date, so the rule check can change after a birthday even though the gap itself never changes.
What Is the Formula?
The age difference and the social rule are two separate calculations.
Exact age difference
- DOBlater: the younger person's date of birth.
- DOBearlier: the older person's date of birth.
- Borrowing: when D is negative, add the days in the previous month; when M is negative, add 12 and take 1 from Y.
Half your age plus seven check
- Aolder: the older person's age in whole years on the selected date.
- ⌊ ⌋: round down, which is how the calculator handles odd ages.
- Ayounger: the younger person's age on the same date.
The rule is a cultural rule of thumb, not a legal or scientific standard, so read the verdict as context rather than approval.
Largest Age Difference the Rule Allows
For common ages of the older partner, this chart shows the youngest partner age that passes the rule and the widest gap it permits.
| Older partner's age | Youngest partner that passes | Largest allowed gap |
|---|---|---|
| 25 | 19 | 6 years |
| 30 | 22 | 8 years |
| 35 | 24 | 11 years |
| 40 | 27 | 13 years |
| 45 | 29 | 16 years |
| 50 | 32 | 18 years |
| 60 | 37 | 23 years |
| 70 | 42 | 28 years |
Values use the calculator's round down step. Anyone under 18 is outside an adult dating range whatever the formula says.
The allowed gap widens with age. That is why the same 10 year difference fails at 30 (a 20 year old is below 22) but passes at 40 (a 30 year old is above 27).
Worked Example
Take two partners born on 15 June 1990 (Person A) and 22 November 1996 (Person B), measured as of 1 January 2026.
- Years: 1996 minus 1990 = 6. Months: 11 minus 6 = 5. Days: 22 minus 15 = 7. Nothing is negative, so the gap is 6 years, 5 months and 7 days.
- Counting every calendar day between the two birthdates gives 2,352 days.
- On 1 January 2026, Person A is 35 (their June birthday hasn't arrived yet) and Person B is 29.
- Rule minimum for the older partner: ⌊35 ÷ 2⌋ + 7 = 17 + 7 = 24.
- Person B's age of 29 is above 24, so the couple sits within the conventional range.
Both birth years fall in the Millennial cohort (1981 to 1996), so the pair is not cross generational. A 6 year gap lands in the 4 to 6 year band, which covers roughly 20% of couples.