What this does
Give it two moments and it tells you how far apart they are, twice over: as a calendar breakdown in years, months and days, and as flat totals in days, weeks, hours and minutes. Both fields take a time as well as a date, so it answers "how old is this" and "how long until launch" with the same arithmetic. It is all local JavaScript — the dates you type stay in the browser and the page works offline.
How do I calculate the days between two dates?
Set both ends and read the totals underneath:
- Set the From and To fields. They start one year apart, from this time last year to right now.
- Use the shortcut buttons if they help: From now and To now stamp the current moment into either field, and Swap exchanges the two.
- Read the headline for the calendar breakdown and the four boxes below it for totals. Order does not matter — the totals are always positive, and a note says whether the target is in the past or the future.
Is the end date included in the count?
No. This measures the gap between two instants, not the number of dates in a range, so it is exclusive of the end. Monday 09:00 to Friday 09:00 comes out as 4 days, not 5. Times matter as well as dates: Monday 09:00 to Friday 08:00 is 3 days, because the totals round down to whole units. If you want the inclusive count — where a Monday-to-Friday week is 5 — use the working days calculator, which counts dates rather than measuring an interval.
How are months and years counted?
By walking the calendar rather than dividing by an average month length. The tool finds the largest number of whole months between the two dates, then reports the leftover days; twelve months become a year. That means the answer matches how people read dates: 15 January to 15 March is exactly 2 months, whatever the length of February in between. Month addition is clamped to the end of the target month, so a span starting 31 January reaches its one-month mark on 28 February, not 3 March.
How does it handle leap years?
Correctly, because every real date in the range is walked rather than assumed. February 29 exists in the count whenever the year has one, so a total-days figure across 2024 is one larger than the same span across 2023. The clamping rule covers the birthday question too: someone born on 29 February hits their anniversary on 28 February in ordinary years, which is the same convention date libraries use. For an age in years, months and days specifically, the age calculator is the focused version of this.
Why do the totals not always agree with the calendar parts?
They measure different things. The calendar parts count real dates; the totals divide the elapsed milliseconds into fixed-length units and round down. A "1 month" span is 28, 29, 30 or 31 total days depending on which month it crossed. Daylight saving shows up here too — a spring-forward day is only 23 hours long, so a span that reads as one calendar day can total 23 hours. If you are comparing moments in different zones, normalise them with the timezone converter first, since both fields here are read in your own local zone.