A business-day calculation is only as reliable as its calendar definition. Weekends are straightforward, but holidays, observed days, regional rules, and the treatment of the start date depend on the purpose of the deadline.
Define the calendar before counting
Write down whether the rule means ordinary Monday-to-Friday weekdays, federal general holidays, a tax authority's public holidays, provincial employment standards, court days, banking days, or an organization's own operating calendar.
Choose endpoint rules
For an interval, decide whether the start date and end date count. When adding days, decide whether a business-day start is day one or whether counting begins on the next business day. A one-day discrepancy often comes from this choice.
Federal and CRA lists serve different purposes
Canada's federal labour-standards page identifies general holidays for federally regulated workplaces. The Canada Revenue Agency publishes its own public-holiday dates, including region-specific entries. Neither should be assumed to govern every provincial, legal, bank, or contract deadline.
Observed and substitute days
When a holiday falls on a non-working day, an applicable rule may provide a substitute day. The built-in presets list published 2026 calendar dates and do not invent substitute-day rules. Verify the rule for the organization or statute involved.
A defensible checking routine
- Identify the authority and exact deadline wording
- Choose and record the calendar
- Record whether endpoints are included
- Add known closures as custom dates
- Keep the result and independently verify consequential deadlines