One tool, two everyday date jobs
Most date questions fall into two buckets, and this calculator covers both. "What date is 90 days from now?" is an add-or-subtract problem. "How long until my lease ends?" is a difference problem. Flip between the two modes with the toggle and the calculator reshapes itself for the task.
Adding and subtracting time
Pick a start date, choose whether to add or subtract, then enter any mix of years, months, weeks and days. The result updates as you type. This is the fast way to answer questions like a 30-day return window, a 12-week training block, a 6-month review date, or a contract that runs two years and three months from signing.
Months and years are handled by the calendar rather than by a fixed number of days, which matters at month boundaries. Adding one month to January 31 lands on the last day of February, not on March 3 — the calculator clamps to the end of the shorter month the way people naturally expect.
Finding the difference between two dates
Switch to difference mode and enter two dates to see the gap expressed several ways at once: an exact years-months-days breakdown plus totals in months, weeks and days. Use it to count down to a holiday, work out how long ago something happened, measure a project's duration, or check how many days are left on a notice period.
A note on counting days
The difference is measured from the start of the first date to the start of the second. So Monday to Wednesday is two days. If your situation counts both the first and last day — for example, billing that includes the start and end date — add one to the total. This "inclusive vs exclusive" detail trips a lot of people up, so it's worth being deliberate about which you need.
Related tools
Working with a birth date instead? The age calculator and chronological age calculator share the same date engine. Expecting a baby? Try the due date calculator.