To find the age difference between siblings, compare their full dates of birth. The sibling with the earlier date is older.
Use the calculator and enter both dates. It will show the gap in years, months and days.
Why their current ages may confuse you
Siblings may say they are 18 and 15 years old. This sounds like a three-year gap. But these are completed ages. The exact gap may include extra months and days.
The fixed age gap comes from the birth dates, not the ages they say today.
Easy steps
- Find both full dates of birth.
- Enter the dates in the calculator.
- Check which sibling is older.
- Read the years, months and days in the result.
Example
The older sibling was born on 12 March 2005. The younger sibling was born on 20 November 2008.
Count from the first date to the second date. The exact gap is 3 years, 8 months and 8 days.
That gap stays the same as both siblings grow older.
Same day and month
If two siblings share the same birthday but were born in different years, the gap is usually a full number of years.
If they were born on the same date in the same year, the date-only difference is zero. For twins, birth times may still be different.
Keep birth dates private
A date of birth is personal information. Share only the result when possible. Avoid posting full dates with names on social media.
Use the Age Difference Calculator