Calendar math without counting on your fingers
Two modes: count the days between any two dates (with weeks and approximate months), or start from a date and jump forward or backward by a number of days — the standard tool for deadlines, notice periods, and return windows.
Frequently asked questions
Are both endpoints counted?
The count is the difference between the dates — Monday to Friday is 4 days. If you need inclusive counting (both days counted), add 1.
Does it handle leap years and month lengths?
Yes — the math uses real calendar dates, so February 29, 30- vs 31-day months, and year boundaries are all handled correctly.
What's the add/subtract mode for?
Deadline math: “45 days from today”, “90 days before the closing date”. Pick a start date, enter the days, choose later or earlier, and get the exact date with its weekday.