Date Duration Calculator

How the Date Duration Calculator Works

Enter a start date and an end date. The calculator returns the gap as total days, then breaks it down into years, months and days, plus equivalent in weeks. Switch to working days mode and it strips out weekends and UK bank holidays, which is number that actually matters for deadlines, deliveries and payroll.

Leap years are handled automatically, including century rules, so a span crossing 29 February counts correctly without you needing to remember which years qualify.

The Counting Question Everyone Gets Wrong

The single biggest source of date errors is whether end date counts. From Monday to Friday is 4 days if you count gap between dates, but 5 days if both ends are included and both answers are correct for different purposes.

The gap counting suits questions like how many days until an event or how old something is. Inclusive counting suits durations of stay, a hotel booking from the 1st to the 5th is 4 nights but 5 calendar days of access and immigration rules counting days of presence in UK include both arrival and departure days. The calculator lets you toggle end date inclusion and for anything legal or official, check which convention rule uses before trusting any tool’s default.

Working Days: the Number Deadlines Run On

Calendar days and working days diverge fast. A 30 calendar day span typically contains only 20 to 22 working days once weekends go and fewer in months carrying bank holidays. That difference is exactly where deadline mistakes happen, because contracts, court deadlines, HR processes and delivery promises are often written in working days while people instinctively count on the calendar.

England and Wales have 8 bank holidays in a normal year, Scotland 9 and Northern Ireland 10 and Christmas period is classic trap, the span from 20 December to 5 January looks like more than two weeks but contains only around 8 or 9 working days. When a deadline matters, count it in working days for the right nation.

Where Exact Day Counts Matter

The situations that bring people to this calculation are rarely casual:

• Notice periods: resignation and tenancy notices measured in weeks or months from a specific date
• Contracts and cooling off periods: 14 day cancellation rights and payment terms in days
• Visas and residency: rules like the 180 days in any 360 for some UK visas or the 90/180 Schengen rule for UK travellers
• Statutory processes: SSP waiting days, probation periods and redundancy consultation windows
• Project planning: durations between milestones in working days

For months based durations there is a quirk worth knowing, a month is not a fixed number of days, so one month from 31 January lands on 28 or 29 February by convention. Where a rule says one month, calendar month convention applies rather than 30 days.

Worked Example

A tenancy notice served on 15 March requiring two full calendar months:

• Two calendar months from 15 March: 15 May
• Total days: 61 in a non leap year
• Working days between the dates: around 42 in England and Wales, fewer if Easter falls inside the span

Run same dates through working days mode and early May bank holiday drops the count by one, kind of single day difference that decides whether a deadline was met.