Date math
Difference = end − start (in days) · Result = start ± amount (days/weeks/months/years)
Day counting is exclusive of the start day (end minus start). Adding months/years lands on the same day-of-month where possible, rolling back for shorter months (e.g. Jan 31 + 1 month → Feb 28/29). Leap years are handled automatically.
Working with dates
Two tools in one: find the exact number of days (and weeks and months) between any two dates, or add and subtract days, weeks, months and years from a starting date to land on a future or past date. Handy for deadlines, anniversaries, contracts and planning.