How to use the date difference calculator
Pick a start date and an end date, and the exact gap between them appears instantly — as a total number of days, as weeks and days, and as a calendar breakdown in years, months, and days. The order does not matter: if the start date is later than the end date, the calculator swaps them for you.
Elapsed days vs. inclusive days
There are two correct ways to count the distance between dates, and choosing the wrong one is the most common source of off-by-one errors. Elapsed counting (the default) measures the time between the dates: Friday to Sunday is 2 days. Inclusive counting counts every date touched, including both endpoints: Friday to Sunday is 3 days. Use inclusive counting when both the first and last day "count" — nights are irrelevant — such as courses of medication, car rentals charged per calendar day, or event durations.
Common uses
This calculator is handy for counting down to a wedding, holiday, or product launch; working out how many days remain until a deadline; measuring the length of a project or contract; checking how many weeks pregnant a due date implies; and settling questions like "how many days have passed since" a memorable date.