ΔtAge & Date Difference Calculator

Counting months between two dates has no single correct answer, and that is not a limitation of this tool.

From 31 January to 28 February is one month by most conventions. From 31 January to 1 March is one month and one day — even though the second span is two days longer. Months have different lengths, so any method of counting them produces an oddity somewhere.

This calculator borrows from the preceding month when the day of month would go negative, which is the convention most people expect and the one used for ages and contract terms. Where precision matters, use the total days figure — that one is unambiguous.

Time zones

Everything is handled in UTC, so results do not shift depending on where you are or whether daylight saving is in effect. A date-difference calculator that uses local time will occasionally be out by a day, and it is always the day that matters.

How age is counted

Completed years. You turn a year older on your birthday and not at any point before it, which is why the years figure only increments on that date rather than rounding.

For someone born on 29 February, most jurisdictions treat the birthday as 1 March in non-leap years for legal purposes, though conventions differ. The day count here is exact regardless of which rule applies.

Reversed dates

Enter them the wrong way round and it compares them the other way and tells you, rather than returning a negative number that you then have to interpret.

Using it for deadlines

Enter today and the delivery date to see the working span. Remember the total is calendar days — subtract weekends and holidays yourself if you are planning actual capacity, or the plan will be optimistic by roughly thirty percent.