Business Days vs. Calendar Days: Which One Contracts Actually Use
Well-drafted contracts specify explicitly whether a deadline is in business days or calendar days, because the two can differ by nearly two weeks over a 30-day period — when a document doesn't specify, many jurisdictions default to calendar days unless context strongly implies otherwise, but this varies and is worth confirming rather than assuming.
The gap between a business-day deadline and a calendar-day deadline is large enough that it genuinely matters which one a contract means — and good drafting reflects that by never leaving it ambiguous.
Why the two diverge so much
A 30-calendar-day period includes roughly 8–9 weekend days, meaning the equivalent 30-business-day period stretches to around 42 calendar days — nearly two additional weeks. For anything with real financial or legal consequences (a notice period, a right to cure a default, a response deadline), that gap is significant enough to matter.
What happens when a document doesn't specify
Practice varies by jurisdiction and context, but many legal systems default to calendar days when a document is silent on which type applies — this is exactly the kind of assumption that's risky to rely on without confirming, since the consequences of guessing wrong on a real deadline can be serious.
This is also why many contracts specifically define terms like "Business Day" in a definitions section — removing the ambiguity by making the convention explicit rather than relying on default assumptions.