How to Calculate Working Days Between Two Dates
Working days — also called business days — are the days on which an organisation operates, typically Monday to Friday excluding bank holidays. Counting them between two dates is necessary for project planning, calculating notice periods, estimating delivery timescales, working out service level agreement (SLA) deadlines, and planning annual leave. Calendar days and working days can differ significantly over any period that spans weekends or public holidays.
Calendar days versus working days
A calendar day count includes every day — weekdays, weekends and public holidays. A working day count includes only the days your organisation treats as working days, typically Monday to Friday, minus any public holidays.
For a two-week period, the calendar day count is 14. The working day count in a standard Monday-to-Friday week with no public holidays is 10. If a bank holiday falls in that period, it becomes 9. The difference matters whenever a deadline, timescale or payment term is expressed in "working days" or "business days".
How to count working days manually
For short periods, counting on a calendar is practical. Mark the start date, step through each day, count only the working days, and stop when you reach the end date. For longer periods — a few months or a year — manual counting becomes error-prone, especially around bank holiday clusters like Christmas and Easter.
A working day calculator automates this by stepping through every day in the range, checking the day of the week, and optionally checking a holiday calendar. The Workday Count tool does this instantly for any date range.
UK bank holidays and their effect on working day counts
England, Wales, Scotland and Northern Ireland have different public holiday calendars, and the differences can be significant. Scotland has two extra bank holidays (2 January and St Andrew's Day) that do not apply in England and Wales. Northern Ireland has additional holidays for St Patrick's Day and the Battle of the Boyne. Always check which calendar applies to the people doing the work.
Around Christmas and Easter, where bank holidays can fall on different days each year, a working day calculator that knows the current year's holiday dates is much more reliable than a manual count.
Calculating a notice period in working days
Employment contracts, tenancy agreements and commercial contracts often specify notice periods in working days. To calculate when a notice period ends: identify the start date (usually the day after notice is given, or the day it is given, depending on the contract wording), count forward the required number of working days excluding weekends and bank holidays, and the end date is the final working day counted.
Example: Notice given on a Friday. Contract requires 5 working days' notice. The following Monday is working day 1, Tuesday is 2, Wednesday is 3, Thursday is 4, Friday is 5. The notice period ends at the close of that Friday — 8 calendar days after the notice was given.
If a bank holiday falls on any of those days, it is not counted, and the notice period extends by one working day for each bank holiday excluded.
Using working days for project planning
Project timelines in working days give a more accurate picture of elapsed time than calendar days, because work only happens on working days. A task estimated at 10 working days that starts on a Monday takes two calendar weeks (assuming no bank holidays). The same task starting two days before a bank holiday takes nearly three calendar weeks.
For projects spanning several months, working day calculations help identify genuine capacity constraints — a team working 5 days per week across a 3-month period has approximately 65 working days available, minus any bank holidays in that period and minus any planned leave.
Service levels and delivery estimates in working days
Customer service SLAs, delivery estimates and regulatory response timescales are frequently expressed in working days. "We will respond within 3 working days" means three Monday-to-Friday days excluding bank holidays — not 72 hours. A contact made on a Thursday afternoon with a 3-working-day SLA would typically be due by the following Tuesday (Friday = day 1, Monday = day 2, Tuesday = day 3), assuming no bank holidays.
Knowing whether a deadline is expressed in calendar days or working days changes the calculation significantly, so always check the relevant contract, regulation or policy for the correct definition.
Common questions about working day calculations
Is the start date counted as a working day?
This depends on the context and the specific rule or contract. Some calculations count the start date as day 1; others start counting from the following working day. Check the applicable wording — this difference of one day can matter for notice periods and deadlines.
What if my organisation works different days?
Not everyone works Monday to Friday. Retailers, hospitals, emergency services and many others operate on different patterns. A working day calculator should allow you to specify which days are working days for your situation rather than assuming a standard Monday-to-Friday week.
Do bank holidays always reduce the working day count?
Only if they fall on a day that would otherwise be counted as a working day. A bank holiday on a Saturday has no effect on a Monday-to-Friday working day count, since Saturday is already excluded.
How do I calculate a deadline that is X working days from today?
Start from today (or the relevant start date), count forward X working days excluding weekends and bank holidays, and the deadline falls at the end of the Xth working day counted. Use the Workday Count tool to do this quickly for any date.
Can working days replace a contractual definition of business days?
No. Contracts can define business days differently — some exclude only weekends, others exclude all public holidays regardless of the location where work is performed, and some have specific lists of excluded days. Always refer to the actual contract wording rather than a general working day calculator for legal or contractual purposes.
Related tools and guides
Use Workday Count to calculate working days between any two dates. For general date calculations including ages and leap years, see Datefully or the date calculations guide. Browse all LibraireStudios guides.
LibraireStudios tools are designed for everyday planning. For contractual, legal or regulatory deadlines, verify the applicable definition of working or business days and the relevant public holiday calendar with the appropriate source.