Age Difference Calculator
Calculate the exact age difference between two people in years, months, and days.
Shows current ages and how old each person was when the other was born.
Age difference calculations determine the gap between two birth dates — useful for family records, medical contexts, legal eligibility, and everyday curiosity.
The calculation: Age difference = Date B − Date A (in years, months, and days)
When both people are alive, the age gap stays constant in years (with occasional day-level variation around birthdays). A person born on 15 March 1985 is always exactly 10 years younger than someone born on 15 March 1975.
Worked examples:
Example 1 — Simple year difference: Person A born: 1 June 1970 Person B born: 1 June 1990 Age difference = 20 years exactly
Example 2 — Crossing months: Person A born: 20 November 1975 Person B born: 5 March 1982 Difference = approximately 6 years 3 months 14 days
Example 3 — Age gap in generations: Grandparent born 1940, grandchild born 2010 → 70 year gap. Average generational gap is 25–30 years, so this represents about 2.5 generations.
Average age differences by relationship:
- Parent to child: typically 25–35 years
- Siblings: typically 1–5 years
- Twins: 0 (or minutes)
- Oldest to youngest in large families: can exceed 20 years
Legal contexts where age matters:
- Driving licence eligibility
- Voting age
- Retirement age calculations
- Age of majority for contracts
- Pension and benefits eligibility
Historical curiosity: The oldest verified age difference between spouses on record exceeds 60 years. The largest recorded verified human age gap between oldest and youngest siblings is over 40 years, in families with multiple marriages.
Age calculations must account for leap years — every 4th year has 366 days rather than 365, which affects precision in day-level calculations.