Date Calculator

About the Date Calculator

Two calculators in one. Difference counts the time between two dates in days, in weeks and days, in months and days, and in years, months and days — plus the number of business days, skipping the weekend days you choose and any holidays you list. Add or subtract finds the date a given number of years, months, weeks and days before or after another date, optionally counting only working days.

For every date you also see its weekday, ISO 8601 week number and day of the year. Everything runs in your browser, and the dates and holiday list never leave your device.

Common uses

• Counting days until a deadline, exam, trip or due date.
• Working out notice periods, leave and delivery times in working days.
• Finding the date 90 days or 6 months from today for visas, warranties and payment terms.
• Looking up ISO week numbers for planning, reports and timesheets.

Should the end date be included?

By default the difference counts the days between the dates, the way you count nights in a hotel: from 1 to 3 October is 2 days. Turn on Include end date when both the first and the last day count, such as leave or an event from Monday to Friday (5 days). Including the end date adds one day to every result, and the business-day count then covers the end date too.

Business days, weekends and holidays

Business days are the days in the range that are not weekend days and not on your holiday list. Weekends differ between countries and workplaces, so you choose them: Saturday and Sunday is the default, Sunday only suits six-day weeks, and Friday–Saturday is common in parts of the Middle East.

Holidays are not built in, because public holidays change by state, by year and by employer — paste the list that applies to you. Accepted formats are 2026-10-02, 02/10/2026 (day/month/year) and 2 Oct 2026, optionally followed by a name. A holiday that falls on a weekend is not subtracted twice.

When adding working days, the start date itself is not counted: five working days after a Friday is the next Friday.

Adding months: the month-end rule

Months have different lengths, so adding months keeps the day number when it exists and otherwise uses the last day of the month: 31 January + 1 month is 28 February (29 February in a leap year), never 3 March. Years work the same way, so 29 February 2024 + 1 year is 28 February 2025. When you add years, months, weeks and days together, years and months are added first and then weeks and days. The result tells you whenever the month-end rule changed the day.

ISO week numbers

ISO 8601 weeks start on Monday, and week 1 is the week that contains the year’s first Thursday. As a result, 1–3 January can belong to the last week of the previous year, and 29–31 December to week 1 of the next. Some years — such as 2026 — have 53 weeks. The ISO week date is written like 2026-W40-5: year, week, then day of the week (1 = Monday).

Limitations

• Dates from year 1 to 9999 are supported, all in the Gregorian calendar (applied to dates before it was introduced, too).
• Public holidays are not included; enter your own list.
• Times of day and time zones are ignored — only calendar dates are counted.

Privacy

Everything is calculated in your browser; the dates and holidays you enter are never uploaded. So that you do not have to paste them again, your holiday list, weekend days and options are remembered in this browser’s local storage — delete the text in the holiday box to remove the list.