Date List Comparison

How to use this calculator

Paste up to 500 ISO dates into each list, separated by lines or commas. Calculate to classify every unique date. Invalid rows must be corrected before a result is produced.

Dates match exactly after strict Gregorian date validation. Duplicate totals count extra occurrences, while another metric counts how many distinct dates repeat. The union and intersection use unique dates; no continuous dates are inserted between entries.

A worked example

List A contains November 1 twice and November 3 once. List B contains November 1 and November 2. There is one shared date, one only in each list, three unique dates overall and one extra duplicate in A.

Can this compare timestamps or date intervals?

This tool compares date-only labels. Use Unix Timestamp Converter for instants or Date Range Overlap for continuous intervals. Mixing dates and times would require an explicit time-zone policy.

Further reading: Source workflow and conventions. Your entered rules determine this result.

Which calendar and years are supported?

Use Gregorian dates from 1900 through 2100, with results inside that range. Most daily plans are limited to 366 dates; academic terms and sprint plans allow up to 731. Forms limit the number of entries to keep calculations responsive. Holidays and policy rules come from your inputs. Date-only plans ignore DST; tools with time-zone inputs use the browser's time-zone data and explicitly resolve repeated times. Calendar exports preserve date-only markers or exact timed events as appropriate. Calculations run only when requested, without background polling.

What happens to my dates?

Calculations run on your device. Saving a calculation is optional and keeps it in this browser. A setup link contains the dates and settings you entered; anyone with the link can read them. Use one tab per saved calculator. Clear saved data from Privacy & settings.