Day Counter Calculator: Days Between Dates, Business Days & Add/Subtract Days
Count days between two dates or add/subtract business days. Include end day, exclude weekends and holidays (US, UK, Canada, custom). Doomsday Algorithm proof. Project timelines, deadlines, notice periods. Free, runs locally, no sign-up.
How Many Days Between Two Dates?
Total days come from the millisecond difference between the two dates (inclusive or exclusive end). Weekday and weekend counts use a constant-time formula from the start date's day-of-week. The calculator's Information Hub above explains Duration mode, Add/Subtract mode, and holiday exclusions in one place.
Business Days vs Calendar Days
Calendar days include every dayโuseful for lease terms, visa validity, or "X days from today." Business days exclude weekends and optionally holidaysโthe norm for project timelines and notice periods. Use Duration Between for the full breakdown; use Add/Subtract with "Count Business Days Only" to step through weekdays only. The Information Hub above summarizes how each mode works.
The Doomsday Rule
The Doomsday Algorithm finds the weekday of any date using a century anchor and a short formula on the year. The calculator's Information Hub includes a Doomsday Rule tile with the formula and a Doomsday Proof tile that runs through the steps for your selected start date.
How to Use the Day Counter Calculator
- Duration Between:Pick start and end dates. Toggle "Include End Day in Count" for inclusive vs exclusive. Read the Day Count Analysis for total days, weekdays, weekends, and holidays.
- Add/Subtract Days:Enter start date and number of days. Choose Add (+) or Subtract (โ). Enable "Count Business Days Only" to skip weekends and holidays.
- Holidays to Skip:Select US Federal, UK, Canada Federal, or enter custom YYYY-MM-DD dates. Excluded dates appear in the Holidays row and are skipped in business-day stepping.
Day Counter Calculator FAQ
How do I count days between two dates?
Use "Duration Between" mode: pick start and end dates. Toggle "Include End Day in Count" for inclusive (both count) or exclusive. The breakdown shows total days, weekdays, weekends, and holidays.
How do I add or subtract business days?
Use "Add/Subtract Days" mode, enable "Count Business Days Only," and enter start date and number of days. The calculator steps through weekdays only, skipping weekends and holidays (US Federal, UK, Canada, or custom YYYY-MM-DD). Good for deadlines, notice periods, and "10 working days from today."
What is the difference between weekdays and business days?
Weekdays are MondayโFriday. Business days are weekdays minus holidays (from Settings). Total days and weekday counts use efficient formulasโno per-day loopโso results are instant. See the Information Hub in the calculator for how each mode works.
How do I exclude custom holidays?
In Settings, choose "Custom dates..." and enter dates in YYYY-MM-DD format (comma or newline separated). Those dates are excluded and listed under Holidays. Also supports US Federal, UK, and Canada Federal.
What is the Doomsday Algorithm?
The Doomsday Rule finds the weekday of any date using a century anchor and a formula on the year's last two digits. The calculator's Information Hub has a Doomsday Rule tile (formula) and a Doomsday Proof tile that shows the step-by-step for your start date.