Working Days Calculator — Business days between dates

Project timelines, invoice due dates, contract deadlines, and delivery estimates all run on working days, not calendar days. Telling a client their project takes "30 days" when you mean 30 working days is a common source of confusion, since 30 working days spans roughly six calendar weeks once weekends are skipped. Knowing exactly how many business days fall between two dates — or exactly which date you land on after adding a number of business days — makes scheduling accurate and professional.

This working days calculator has two modes. In "Count days in range" mode, it walks the calendar day by day from your start date to your end date, classifying each date as a weekend day, a custom excluded day, or a working day, and tallies each bucket separately so you can see total calendar days, weekend days removed, and custom days removed alongside the final net working day count. In "Add working days" mode it works in reverse: starting from your chosen date, it steps forward one calendar day at a time and only counts a day toward your target once that day passes the same working-day test, stopping as soon as the requested number of working days has been reached and reporting both the resulting end date and how many calendar days actually elapsed to get there.

By default Saturday and Sunday are excluded, but each can be toggled independently, so a Sunday-only weekend or a Monday-to-Saturday six-day work week is just as easy to model as the standard five-day week. Beyond weekends, you can paste a list of custom exclusion dates in YYYY-MM-DD format, one per line — office closures, company holidays, or personal days off — and every one of those dates is subtracted from the count the same way a weekend day is, tracked in its own "custom days excluded" row so you can see exactly how much a holiday schedule shifted your deadline.

A common hand-calculation mistake is subtracting calendar days by weeks (dividing by 7 and multiplying by 5), which breaks down as soon as the range does not start on a Monday or a holiday falls inside it; walking day by day avoids that error entirely. Everything runs client-side in your browser, so no dates are ever sent to a server.