How it is worked out
years = whole months between the two dates ÷ 12
Why it is done this way
Years are not counted by dividing days by 365. Between 2020 and 2024 there is an extra 29 February, so that division drifts. The correct method is to step month by month from the first date and see how many whole years fit before overshooting.
Step by step
- Start from the earlier date
- Step forward year by year while you do not pass the later date
- The years you managed to step are the whole years
- What is left from there to the final date are the extra months and days
What is worth knowing
The gap between whole years and decimal years matters more than it looks. Length of service and legal limitation periods run on completed years, and at eleven months there is still no year; comparing returns or growth uses decimal years, because an eleven-month period really does contribute eleven twelfths. This page gives both, so you do not have to guess which one your case needs.