Date Calculator
Add or count dates with custom weekends, excluded dates, endpoint rules and a CSV breakdown.
This tool runs entirely in your browser. Your data is never uploaded, never stored, and never leaves your device.
Add or subtract dates and count working days with custom weekends, excluded dates, explicit endpoint rules and CSV output.
How to use it
- 1Enter complete start and end dates, or an amount and direction.
- 2Choose weekend weekdays, exclusions and the endpoint rule.
- 3Calculate, review the day breakdown and copy or download the assumptions.
What happens to your data
Dates and exclusion lists are calculated in your browser, without uploads, automatic holiday lookups or URL storage.
Last updated October 2026
Add or subtract calendar days, working days, weeks, months or years, or count an interval between two dates. Choose weekend weekdays and supply your own excluded dates, such as an office closure or school holiday. Results show readable weekdays and separate totals for counted calendar days, working days, weekends and additional exclusions. Open the date-by-date breakdown to see exactly which dates were counted, skipped or ruled out by the endpoint settings. Copy the explanation, download the summary CSV or keep the detailed date classification as a separate CSV.
A working day has no universal meaning. Some teams work Monday to Friday, others have a six-day week, and some use Friday and Saturday as their weekend. Saturday and Sunday are selected initially but can be changed. Holidays are not guessed or downloaded, and a result is not certified as a legal deadline. Date-by-date auditing is limited to spans of 10,000 days, with 31 rows previewed and the complete supported breakdown in its export; longer calculations still retain the original 366,000-day totals limit. Inputs and rules stay locally in the browser and are not added to the page URL.
How it works
Enter complete dates as YYYY-MM-DD, using years 0001–9999. The calendar uses the Gregorian rules throughout, including dates before a country historically adopted that calendar. Invalid dates such as 2026-02-30 receive an error rather than rolling into March or silently becoming today. Arithmetic uses whole calendar days, so a daylight-saving transition does not make a day count as 23 or 25 hours. This tool handles dates, not elapsed timestamps; use the Timestamp Converter or Timezone Converter for clock times.
Add/subtract always excludes the starting date and includes the result date. Adding zero leaves the starting date unchanged and counts zero days. Adding working days walks in the selected direction, skipping the weekend weekdays and excluded dates you provided. An excluded date that already falls on a weekend is counted as a weekend once, not subtracted a second time. Duplicate excluded dates also count once. Exclusions outside the interval are retained in the downloaded assumptions but do not change the answer.
Between dates gives you separate switches for including the start and end. These refer to the dates as entered, even if the end is earlier than the start. Results are counts rather than negative durations, and the explanation identifies a backwards interval. For the same date, one day is counted only if both endpoints are included. Clearing either endpoint produces zero. This explicit convention prevents a same-day interval from being counted twice.
Months and years preserve the day number where it exists. Otherwise the result uses the last valid day of the destination month: 2026-01-31 plus one month is 2026-02-28, and 2024-02-29 plus one year is 2025-02-28. The result discloses that adjustment. Each amount must be an integer from zero to 100,000; the overall interval is limited to 366,000 days and the exclusions list to 500 dates. Larger requests are rejected, never silently reduced. Copy and CSV exports preserve the endpoint convention, weekend names and supplied excluded dates for review.
Worked example: five working days with one closure
- Input
- Start 2026-10-05; add 5 working days; skip Saturday/Sunday; exclude 2026-10-07
- Result
- 2026-10-13 — 8 calendar days, 5 working days, 2 weekend days and 1 additional excluded day
The start is excluded and the result is included. October 7 is the user-supplied closure, not an automatically detected public holiday.
Common use cases
- Planning a task around a custom working week
- Checking the number of available school or office days
- Keeping an auditable calculation with a project schedule
- Comparing inclusive and exclusive date intervals
- Adding months to an end-of-month calendar date
Frequently asked questions
Can I see which individual dates made up the answer?＋
Yes. Open Check each date after calculating. Each date is marked as a working day, weekend day, additional excluded day or an endpoint not counted. The preview shows up to 31 rows; its separate CSV includes the complete breakdown for spans up to 10,000 days. Longer intervals still receive totals, but no partial breakdown export is presented as complete.
What do the example and Swap dates buttons change?＋
The example deliberately replaces the current settings with five working days from October 5, 2026, excluding October 7 and Saturday/Sunday. Swap dates exchanges the entered start and end in Between dates mode. The include-start and include-end switches continue to refer to their labeled input fields. Editing clears the prior calculation and downloads.
Does the business day calculator automatically exclude public holidays?＋
No. Enter the specific dates you want to exclude. This avoids assuming that a national holiday, regional observance or company closure applies to your schedule. Check your own calendar before using the result.
Are the start and end dates included?＋
Add/subtract excludes the start and includes the result. Between dates has separate switches for each endpoint. A same-date interval counts one day only when both switches are selected.
Can I use a Friday–Saturday weekend or a six-day working week?＋
Yes. Select any weekend weekdays, or none. At least one weekday must remain available as a working day. Your choices are included in the copied explanation and CSV.
Why does adding one month to January 31 give February 28?＋
February 31 does not exist. This tool clamps to the last valid day of the target month and tells you it did so. Leap-year February has 29 days. This is a stated calendar convention rather than a promise about any contract or official rule.
What happens when the second date is earlier?＋
The calculator walks backwards, still applying include-start and include-end to the original entered dates. Counts stay nonnegative and the explanation says that the end date is earlier.
Standards and limitations
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