An exact age difference is usually shown in three parts: years, months and days. These parts work together to show one complete gap.
Try the calculator with two dates of birth to see this result.
What the years mean
The year number shows how many full calendar years fit between the two dates.
If the older person was born on 10 May 1990 and the younger person was born on 10 May 1995, the gap is exactly 5 years.
If the later date is before 10 May in 1995, five full years have not finished. The year part would still be four.
What the months mean
After counting the full years, we count the full months that are left.
Months do not all have the same number of days. February is shorter than March. So, we count real calendar months instead of using 30 days for every month.
The month part is the number of full months left after removing the full years. It is not the total number of months in the whole gap.
What the days mean
After counting full years and full months, a few days may still be left. These become the day part of the answer.
For example:
3 years, 2 months and 6 days
This means you move forward 3 full years, then 2 full months, then 6 days to reach the later date.
Worked example
Compare 18 September 1987 with 3 February 1992.
- Four full years take us to 18 September 1991.
- Four full months take us to 18 January 1992.
- Sixteen days take us to 3 February 1992.
The exact age difference is 4 years, 4 months and 16 days.
This example crosses months with different lengths. Counting calendar steps avoids guessing how many days an average month contains.
Exact gap and total days are different views
The answer in years, months and days is easy to understand. The total-day answer is useful when you need one number.
Both can be correct. They simply show the same gap in different ways.
You cannot safely convert the month part to days by multiplying it by 30. Four calendar months may cover 120, 121, 122 or 123 days, depending on the dates involved.
Exact age gap and completed ages
The exact date-to-date gap is fixed. The difference between two completed ages can appear to change during the year.
For example, a fixed gap of 4 years and 4 months may temporarily look like five years when only one person has had a birthday. Compare the birth dates when you need the true gap.
A quick check
If the result says 12 months or more in the month part, something is wrong. Twelve full months should become one full year. The month part should normally stay between 0 and 11.
Also check that the day part is reasonable for the month being crossed. If the result came from a spreadsheet, confirm that both cells contain real dates and not plain text.
Use the Age Difference Calculator with the same dates and confirm that moving forward by the displayed years, months and days reaches the later date.
Use the Age Difference Calculator