Irish Calculators
Work & pay

Add or Subtract Business Days Calculator

Find the date a stated number of business days before or after your starting date. Choose the working week and supply observed closures; the starting date is day zero.

Runs privately in your browserMethod reviewed

Your numbers

One YYYY-MM-DD per line. Add public holidays or closures that your business actually observes.
Your figures stay on this device.

How the calculation works

Add or subtract a stated number of business days from a starting date. The starting date is always day zero, and the tool moves through the calendar until it has counted the requested number of eligible dates.

The starting date is day zero. Move forward or backward one date at a time and count only dates in the working week that are not excluded.

  1. Begin after or before day zero

    For a non-zero request, first move one calendar date in the selected direction. The starting date is never counted as the first business day.

  2. Count only eligible dates

    A date reduces the remaining count only when it belongs to the selected working week and is absent from the closure list.

  3. Stop on the final counted day

    Continue across weekends and exclusions until the count reaches zero. The result is the date of that final eligible day, not a sum of fixed 24-hour working blocks.

Worked example: Weekend crossing

Sample inputs demonstrate the method. They are not a forecast or product offer.

The first example begins on Friday 2 October 2026 and adds one business day under a Monday-to-Friday pattern. Saturday and Sunday are skipped, so the first counted day is Monday 5 October 2026.

Starting date
2026-10-02
Business days to add or subtract
1
Working week
Monday to Friday
Additional non-working dates

Expected result

Resulting date
2026-10-05
Worked example: Backward crossing

Sample inputs demonstrate the method. They are not a forecast or product offer.

Starting date
2026-10-05
Business days to add or subtract
-1
Working week
Monday to Friday
Additional non-working dates

Expected result

Resulting date
2026-10-02

Understanding your result

Subtracting business days is useful for working backwards from a required date, using the same holiday and closure assumptions. The direction changes, but the eligibility test stays the same.

This is date-only arithmetic on a UTC calendar. It does not evaluate cut-off times, delivery hours, statutory deadline extensions or a bespoke rotating roster.

Questions you might have

What does this add business days calculator include?

Add or subtract working days from a date using your working week and an explicit list of holiday or closure dates.

Which assumptions should I check?

Enter the holiday and closure dates relevant to your business. Zero business days returns the start date even when it is not a working day.

Choosing the right inputs

Business days to add or subtract
Enter a whole positive number to move forward or a negative number to move backward. Zero returns the start unchanged, even when it is a weekend or closure.
Working week
Choose Monday to Friday, Monday to Saturday, or every day. The same selected pattern applies throughout the calculation.
Additional non-working dates
List observed holidays and closures using YYYY-MM-DD. These dates must come from the calendar relevant to your deadline or workplace.

Common mistakes to avoid

  • Do not count the start manually and then enter the full count here; that would shift the result.
  • A public holiday is not excluded unless it is outside the chosen week or explicitly appears in your closure list.

Assumptions to check

  • Enter the holiday and closure dates relevant to your business. Zero business days returns the start date even when it is not a working day.

Sources and method

Read our calculation and testing approach.