Working days versus calendar days, and what contracts mean

"Within ten days" and "within ten working days" look like small variations of the same clause. They are not. Ten calendar days is a fortnight minus a bit. Ten working days is two full weeks of business, and with a public holiday in the middle it can stretch past a fortnight. Contracts, refunds, notice periods and service levels all live on this distinction.

What each one counts

• Calendar days count every day, weekends and holidays included. Simple, predictable, and indifferent to where the parties are.
• Working days count only days on which business is normally done. In most of Europe and the Americas that means Monday to Friday, excluding public holidays.
• Business days in a specific market can be narrower still, excluding bank holidays or exchange closures that are not general public holidays.

The clauses worth reading twice

Three details decide the actual deadline, and they are usually buried:

• Does the clock start on the day of the event or the day after? "Within five working days of receipt" usually starts the next working day, but not always.
• Whose holidays count? A contract between parties in different countries has to name a jurisdiction, or the two sides will compute different deadlines in good faith.
• What happens when the last day is not a working day? Most rules roll the deadline forward to the next working day. A few roll it back. The difference can be three days over a long weekend.

A rough conversion, and why to distrust it

Working days run at five per week, so ten working days is about fourteen calendar days and twenty is about twenty-eight. That approximation is fine for planning and wrong for deadlines, because it ignores holidays entirely. In periods dense with them, such as late December in much of Europe or a run of national holidays elsewhere, the same count of working days can span several extra calendar days.

Write it so nobody has to interpret it

The cleanest form states the count, the type of day, the starting rule and the jurisdiction in one sentence: "within ten working days (Monday to Friday, excluding public holidays in Denmark), beginning the first working day after receipt". Then give the resulting calendar date in the covering email, because a date cannot be misread and a rule can.

To turn the rule into that date, the business days calculator counts Monday to Friday between two dates, which is the base case most contracts start from before local holidays are applied.