How to Calculate a Deadline Date Correctly

To calculate a deadline date, you need to know three things: the start date, the number of days, and whether you're counting calendar days or business days.

The phrase "within X days" typically means you have until the end of day X, not the start of day X.

Inclusive vs Exclusive Counting

The biggest source of deadline confusion is whether the start date counts as day 1 or day 0:

• Inclusive: The start date is day 1. "Within 3 days of Monday" means by Wednesday.
• Exclusive: Counting starts the day after. "Within 3 days of Monday" means by Thursday.

Legal deadlines often use exclusive counting—the clock starts the day after the triggering event.

Try our Deadline Calculator to find the exact due date for any deadline.

Business Days vs Calendar Days

Always check whether a deadline is measured in:

• Calendar days: Every day counts, including weekends and holidays
• Business days: Only weekdays (excluding public holidays) count

A "5-day deadline" could end on very different dates depending on this distinction.

Common Deadline Phrases

Here's what common phrases typically mean:

• "Within 30 days": Usually 30 calendar days from the trigger date
• "5 business days": 5 weekdays, skipping weekends and holidays
• "By close of business": Usually 5:00 PM or 6:00 PM local time
• "End of day": Midnight or 11:59 PM

When Deadlines Fall on Weekends

If a deadline falls on a weekend or holiday:

• Legal deadlines often extend to the next business day
• Contract deadlines may or may not extend—check the terms
• Tax deadlines typically extend to the next business day

Avoid Deadline Mistakes

The safest approach is to finish early. If you're unsure about inclusive vs exclusive counting or business vs calendar days, give yourself a buffer.