Enter two birthdays. You will get exact years, months, and days between them, along with total days and weeks. We also show who is older, next birthdays, weekdays born, and half-birthdays.
Inputs
Defaults to today in your browser time zone
Summary
Age and difference summary
Who is older
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Exact difference
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More details
Birthdays, next birthdays, and half-birthdays
Item
Value
Notes: For Feb 29 birthdays we use your chosen rule when finding the next birthday in non-leap years.
How to use this age difference calculator
Enter the names (optional) and birth dates for Person A and Person B.
(Optional) Pick an “As of” date if you want the age difference on a specific day. Otherwise we use today.
Choose how to treat Feb 29 birthdays (Feb 28 vs Mar 1) for non-leap years.
Click Calculate. The summary shows who is older and the exact difference in years, months, and days.
Tip: Use Swap A and B to quickly flip the inputs, and Download CSV to export the results.
What your result means
This tool does two things: it identifies who is older and computes the exact difference between the birthdays using calendar math. That means it respects real month lengths and year boundaries instead of assuming every month has the same number of days. You also get total days and weeks for quick “how far apart” comparisons.
Who is older: Determined by the earlier birth date.
Exact difference: Years, months, and days between the earlier and later birth date. When a target month lacks the same day number, the calculation uses the last valid day.
Leap years: Feb 29 birthdays are handled with your preference for non-leap years (Feb 28 or Mar 1). Next birthdays and half-birthdays follow the same rule.
Half-birthday: Six months after the birthday within the current cycle; adjusted for month length.
This is for planning and general use. For legal needs, verify dates with official documents.
FAQ
Is this calculator accurate for leap years?
Yes. We handle Feb 29 birthdays and let you choose whether to celebrate on Feb 28 or Mar 1 in non-leap years.
Why do months sometimes look short or long in the breakdown?
We use true calendar math. When a month doesn’t have the same day number, we adjust to the last valid day.
Can I compare ages on a past or future date?
Yes. Set the “As of” date to any day to see the age difference on that specific date.
What’s the difference between total days and exact Y-M-D?
Total days is a straight day count. The Y-M-D breakdown follows calendar boundaries (years, months, days).