Date Range Overlap Calculator

How to use

1. 1Pick a precision mode: date only for vacations and contracts, or date and time for shifts and meetings.
2. 2Choose the boundary mode: inclusive end for calendar-style ranges, exclusive end for half-open [start, end) ranges.
3. 3Enter at least two ranges with a start and end. Optionally label each range so the results read naturally.
4. 4Read the summary card for overlapping pair count, the common slice every range shares, and the merged union with any gaps.
5. 5Open the pairwise analysis to see every pair's Allen relation, overlap duration, and the exact overlap range.
6. 6Copy the report to paste a full plain-text summary into a project plan, ticket, or email.

About this tool

Date Range Overlap Calculator answers the practical question of whether two or more date ranges share any time, and if they do, exactly how much. Add up to ten ranges (each with an optional label, a start, and an end), and the tool checks every pair, reports the overlap duration, names the relationship using one of the thirteen Allen interval relations (before, after, meets, met-by, overlaps, overlapped-by, contains, during, starts, started-by, finishes, finished-by, equal), and shows the exact overlap range. A summary panel reports how many of the pairs overlap, the common slice every range covers (when one exists), and a merged union of every range so you can see total coverage and any gaps as separate segments. A boundary toggle lets you switch between inclusive ends (Mar 3 to Mar 5 covers Mar 3, 4, and 5; touching counts as overlap) and exclusive ends (half-open [start, end); touching counts as meets, not overlap), matching the convention used by calendars and hotels versus the convention used by most programming libraries. A precision toggle switches between date-only ranges, which is ideal for vacations, contracts, leases, and project phases, and date and time ranges down to the minute, which is ideal for work shifts, room bookings, and meeting calendars. Built-in examples cover overlapping PTO requests, back-to-back rental contracts, two work shifts on the same day, and three overlapping project phases with one gap. A copyable report summarises the inputs and every result so you can paste it straight into a project plan, an email, or a ticket. Useful for project managers checking phase conflicts, schedulers and HR teams reviewing PTO double-booking, hotel and rental operators validating reservation windows, lawyers and operations reviewers checking contract validity periods, ops teams looking for shift coverage gaps, and developers debugging temporal predicates in SQL or in code. All math runs locally in your browser. Schedule data is never uploaded.

Free to use. Works in your browser. No signup, no login.