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About this tool
Find the exact age gap between two people in years, months and days, plus total weeks and days.
Age Difference Calculator works out the exact gap between two dates of birth in years, months and days, and backs it up with the total days, weeks and months between them. It counts calendar-style — full years first, then whole months, then the leftover days — so leap years and 28-to-31 day months are handled correctly instead of being averaged away. You can also pick any reference date to see how old each person is on that day.
Open Age Difference Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Months are counted as real calendar months and leap days are included, so the answer matches how people actually count age.
Get years-months-days plus total days, total weeks with leftover days, total months and a decimal-years figure.
Set the 'as of' date to today or any past or future day to see both ages side by side.
The calculator counts the largest number of whole calendar months that fit between the two dates, then adds that many months to the earlier date (clamping to the last day of the target month, so 31 January plus one month lands on 28 or 29 February). Whatever days are left over after that point become the day count. This calendar-anchored approach is why month-end dates such as 31 January to 28 February come out as '1 month, 0 days' rather than '0 months, 28 days'.
No. The calculator detects which date is earlier and always reports a positive gap, labelling who is older. A swap button is there if you simply want to flip the two entries.
Because calendar months differ in length. A gap that spans February will show different leftover days than one spanning July. The total-days figure never changes for the same interval, which is why it is shown alongside.
Yes. February 29 is counted as a real day, and dates in leap years are validated properly, so the total-days figure is exact.
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