Business Days vs. Calendar Days: How to Count Deadlines
October 21, 2026
Calendar days count every day, including weekends and holidays. Business days count only working days, usually Monday to Friday excluding public holidays. As a rule of thumb, multiply business days by 7/5 to estimate calendar days: 10 business days is about 14 calendar days, and 30 calendar days is about 21 business days. In 2026, there are 261 weekdays, before removing holidays.
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Open the Date Calculator →Converting Between Them
A week has 5 business days and 7 calendar days. For 10 business days starting on a Monday, the 10th business day is the second Friday, so the period spans two full calendar weeks. Starting midweek changes the result because weekends fall in different places: ten business days from a Wednesday runs through the Tuesday of the third week.
Public holidays remove more days. In the US, there are 11 federal holidays; the UK has 8 bank holidays in England and Wales. A 20-business-day period can stretch to 29 or 30 calendar days when it includes a holiday.
| Business days | Approximate calendar days | Notes |
|---|---|---|
| 5 | 7 | One week |
| 10 | 14 | Two weeks |
| 20 | 28 | Add a day or two per holiday |
| 30 | 42 | About six weeks |
| 60 | 84 | About twelve weeks |
Counting Rules in Contracts
Contracts and regulations define their own conventions. Some count the day of the event as day zero, some count it as day one. Some define business days as excluding only weekends, and others exclude local holidays or bank closing days. Shipping carriers often exclude Sundays or have different weekend rules.
When a deadline falls on a weekend or holiday, rules vary. Many legal systems roll it to the next business day, but not all, so check the wording.
Practical Tips
Write dates unambiguously and state whether the period includes weekends. When promising delivery in a number of business days, count from the next business day after an order placed after cut-off time.
Use a date calculator or spreadsheet function such as NETWORKDAYS or WORKDAY with a holiday list to avoid manual mistakes.
Frequently Asked Questions
How many business days are in a year?
Roughly 260 to 261 weekdays, and about 250 after typical public holidays.
Is Saturday a business day?
Usually not, but some industries and countries count it. Check the definition used in your contract.
How many calendar days is 15 business days?
About 21 calendar days, or three weeks, ignoring holidays.
How do holidays affect the count?
Each holiday on a weekday removes a business day, extending the number of calendar days.