Missing Date Finder

Find missing dates in a pasted list against a daily, selected-weekday or every-N-days calendar. Report duplicates, invalid rows and unexpected dates.

Starts with an editable example. Replace the dates and rules with your own.

Your calculation

Ready when you are

Choose your dates.

Select your counting rules and calculate.

How to use this calculator

Choose an inclusive range of up to 366 dates, expected cadence and optional closures. Paste up to 100 observed date rows in a declared format.

Expected dates are compared with unique valid observed dates. Repeated observations do not fill extra gaps. Dates outside the expected calendar remain visible, and public holidays are excluded only when entered by you.

A worked example

For November 2-8, 2026, observations on November 2, 3 and 5 leave four dates missing from a daily calendar.

Will it detect duplicate dates written differently?

Rows use one declared format. Valid rows are normalized before comparison, so identical dates count once and repeats are reported.

Which calendar and years are supported?

Each result states its calendar, time scale, precision and supported range. Batch converters accept up to 100 nonempty input lines and retain invalid rows. Copy, CSV and print include the calculation rules. Calendar downloads appear when a result contains dated events. Calculations run in your browser; no reminders or jobs are scheduled.

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.