How to Add, Subtract and Compare Calendar Dates

Make the counting rule explicit when calculating a period between two dates.

Use the Date Calculator alongside this illustrative example.

A practical example

From 1 March 2026 to 8 March 2026 there are seven elapsed calendar days. Counting every date on a checklist, including both endpoints, gives eight dates instead. Those are different questions, so write down which one your deadline or report requires before interpreting the answer.

Check the result

Use the days result for an exact interval; month and year summaries may be approximate. When adding months near month-end, inspect the returned calendar date rather than assuming it stays on the last day of the destination month.

Try a comparison

Repeat the date difference with a pair spanning a weekend. The elapsed days still include Saturday and Sunday. If the task instead counts working days, make a separate calendar checklist with local holidays rather than silently subtracting every weekend.

What this does not establish

The tool is not a business-day or holiday-calendar service. Contracts can define their own counting and timezone rules.

Report unclear guidance or a result that needs checking.