Add Days to a Date – Date Calculator (Days, Weeks, Months)

Add or Subtract Days

Add or subtract days, weeks, months or years from a date, in calendar days or business days with Canadian or US holidays. See each step of the calculation.

Start date

Operation Add Subtract

Years Months Weeks Days

Count days as

Result

–

ISO date: –
Day of the week: –
Calendar days from the start date: –

Steps

How to add or subtract days

Choose the Start date (today by default; the Today button resets it).
Pick Add or Subtract under Operation.
Enter the amounts in Years, Months, Weeks and Days. You can combine them, for example 1 month and 10 days. Empty fields count as zero.
Under Count days as, keep Calendar days, or choose Business days to skip weekends and public holidays. Then pick the Public holidays calendar: Canada (federal), a province or territory, the United States (federal), or None (weekends only).

The Result appears as you type, with the ISO date (YYYY-MM-DD), the Day of the week and the number of Calendar days from the start date. The Steps list shows how the date was reached.

How the calculation works

The amounts are applied in a fixed order, which matters when months are involved:

Years and months are added together, as a number of months (1 year and 2 months = 14 months). The day of the month stays the same when it exists. When it doesn’t, the date is moved to the last day of the month: January 31 + 1 month = February 28 (or 29 in a leap year), and February 29, 2024 + 1 year = February 28, 2025. The steps tell you when this happens. Adding years and months in one go avoids clamping twice.
Weeks are always 7 calendar days.
Days are then added, either as calendar days or as business days.

In Business days mode, the start date itself isn’t counted, like the WORKDAY function of spreadsheets: adding 1 business day to a Friday gives the next Monday, or Tuesday if Monday is a holiday. Days that are Saturdays, Sundays or holidays of the chosen calendar are skipped, and the step shows how many were skipped. Holidays are computed from their legal rules (Easter, “Monday before May 25”, “second Monday of October”…) with the same engine as the business days calculator, including substitute days when a holiday falls on a weekend.

Examples

90 days from September 29, 2026 is December 28, 2026.
30 days before March 15, 2026 is February 13, 2026 (February has 28 days).
January 31, 2026 + 1 month is February 28, 2026 (clamped to the end of the month).
10 business days after December 18, 2026 in Ontario skips December 25 (Christmas), December 28 (Boxing Day falls on a Saturday and is moved to Monday) and January 1 (New Year’s Day), and lands on January 6, 2027.

Typical uses: a return or cancellation deadline, the due date of an invoice at 30 or 60 days, the end of a probation period, a notice period in business days, or the date that is “6 weeks from today”.

Frequently asked questions

Is the start date counted?

No. Adding 1 day to Monday gives Tuesday. To count the start date as day 1, subtract one day from the amount.

Why does adding one month to January 31 give February 28?

February has no 31st, so the result is clamped to the last day of the month, which is the most common convention (used by spreadsheets and most programming languages).

What is the difference with the business days calculator?

This tool finds a date from a number of days. The business days calculator does the opposite: it counts the business days between two dates.

Which holidays are used for business days?

The general holidays of the chosen jurisdiction’s employment standards law, or the 11 US federal holidays. For custom closures or a different weekend, use the business days calculator, which supports both.

How far can I go?

Up to 10,000 days or weeks and 1,000 months or years, for results between years 1 and 9999 of the Gregorian calendar.