How to Calculate Days Between Two Dates
Calculating the number of days between two dates is one of those everyday problems that sounds simple until you start counting weekends, bank holidays, and leap years. Whether you're tracking a project deadline, planning an event, or working out your notice period, getting the exact figure matters. Use our days between dates calculator for instant results, or read on to understand how it works and handle the trickier cases.
Why calculating days between two dates matters
You're not counting days for fun. You're counting down to something specific—a project deadline, a holiday, a contract end date, the gap between two milestones. Get the number wrong by a day or two, and your planning falls apart.
Here's where precision saves you:
Project deadlines — your report is due on the 15th. You need 3 days for review, 5 working days to write it, 2 days for planning. Work backwards: start by the 5th. But if you miscalculate weekends, you've lost 2 days. Use our days between dates calculator to find the exact window.
Notice periods — if you're leaving a job, your contract specifies notice in days or weeks. Give notice on the 1st with 2 weeks required? Your last day is the 15th. Miss this and your employer can dispute the resignation. See our guide on calculating notice periods and end dates for the full breakdown.
Event planning — a wedding 200 days away, a birthday party, a conference. The number of days left determines how many weeks you have to book venues, send invites, and sort logistics.
Contractual timelines — a 365-day lease, a 90-day trial period, a 12-month payment plan. Knowing exactly when a contract ends prevents disputes and surprise charges.
Annual leave — you want to book a 2-week holiday. Does your employer count working days or calendar days? The difference between 14 and 10 days is substantial when you only get 25 days a year.
How to calculate days between two dates
The simple version: count every day from start to end, including both dates. That's what the calculator does.
If you want to do it manually, you need to account for the structure of the calendar. A year has 365 days (or 366 in a leap year). Months have between 28 and 31 days. Weeks have 7 days.
Example within a single month:
- 1 March to 15 March = 15 days (including both the 1st and the 15th)
- 10 March to 20 March = 11 days
Example across months:
- 15 March to 22 April involves:
- Days left in March: 31 − 15 = 16 days (March 15–31)
- Days in April: 22 days (April 1–22)
- Total: 16 + 22 = 38 days
Example across years:
- 1 December 2025 to 31 March 2026 involves:
- Days left in December: 31 (Dec 1–31)
- Days in January 2026: 31
- Days in February 2026: 28 (2026 is not a leap year)
- Days in March: 31
- Total: 31 + 31 + 28 + 31 = 121 days
This is why a calculator is faster and more reliable than working it out by hand. There are too many boundary conditions to miss.
Working days, weekends, and bank holidays
Here's where most people's mental maths breaks down. A "30-day" deadline sounds like a month. But 30 calendar days includes weekends. If a project is due in 30 days and you're counting only working days (Monday–Friday), you have roughly 22 working days—a 27% reduction.
Add UK bank holidays, and the number shrinks further. Between early May and late May, there are two bank holidays: Early May Bank Holiday (first Monday) and Spring Bank Holiday (last Monday). If your deadline falls in that window, you lose 2 additional working days.
Rough maths:
- 30 calendar days = roughly 4 weeks
- 4 weeks = 20 working days (Monday–Friday)
- Minus 2 bank holidays = 18 working days
Real example: report due Friday 30 May 2026, starting Monday 18 May:
- Week 1 (18–22 May): 5 working days
- Monday 25 May: Spring Bank Holiday, so 0 days
- Week 2 (26–29 May): 4 working days (Tues–Fri)
- Friday 30 May: 1 day
- Total: 5 + 0 + 4 + 1 = 10 working days
If you need to count weeks instead of days, our guide on calculating weeks between dates breaks it down further.
Practical scenarios
Scenario 1: Planning a holiday
You're booking 2 weeks away. Today is 15 April 2026, and you want to leave 20 May – 3 June. How much leave do you need?
Calendar days: 15 May to 3 June = 20 days. But 2 days fall on weekends (Sunday 24 May, Sunday 31 May). If your employer counts only working days, that's 14 working days of leave. If they count calendar days, it's 20. Check your contract.
Scenario 2: Project deadline across a bank holiday
Kickoff: Monday 4 May 2026. Deadline: Friday 29 May 2026. The Spring Bank Holiday falls on Monday 25 May.
Calendar days: 20 days. Minus weekends (4 Saturdays and 4 Sundays): roughly 14 working days. Minus 1 bank holiday: 13 working days. If you'd naively assumed 20 days = 4 weeks = 5 working days a week, you'd be way off. You actually get 2.6 working days a week.
Scenario 3: Resigning with notice
Today is 15 April 2026. Your contract says "4 weeks' notice". What's your last day?
4 weeks = 28 calendar days. 15 April + 28 days = 13 May 2026. Your employment ends on 13 May. (If your contract said "30 days' notice", it would be 15 May instead.)
The difference looks small, but it matters. See our full guide on calculating notice periods and end dates for edge cases and sector-specific rules.
Scenario 4: Age differences
Someone asks "how many days apart are you and your sibling?" If you're born on 15 March 1992 and they're born on 3 August 1995, the gap is 1,836 days (or 5 years and 141 days). We have a guide on calculating age difference between two people if you need it.
Beyond simple day counting
Leap years — a leap year has 366 days instead of 365, with February having 29 days instead of 28. 2024 was a leap year. 2025 and 2026 are not. If your date range spans February in a leap year, you gain an extra day. The calculator handles this automatically.
Day of the week — sometimes you need to know which day a date falls on. "The deadline is the 15th—is that a Friday?" We have a day-of-the-week calculator for this.
Adding or subtracting days — if you need to calculate "30 days from today" or "2 weeks before the deadline", our guide on adding or subtracting days from a date covers the logic.
Your exact age — if you need your age not just in years but in years, months, and days, our age calculator shows all three. This is useful for insurance quotes, medical forms, or curiosity.
Planning with multiple deadlines — if you're managing a year with many key dates and deadlines, see our guide on planning your year with key dates and deadlines for how to structure it.
Frequently Asked Questions
Q: Does the calculator include the start date and end date? A: Yes, it includes both. So 1 January to 3 January = 3 days (the 1st, 2nd, and 3rd). Some people count only the days in between (2 days). Always clarify with whoever set the deadline—"due by the 15th" usually means the end of the 15th.
Q: What's the difference between calendar days and working days? A: Calendar days include every day: weekends and bank holidays. Working days (or business days) count only Monday–Friday, excluding bank holidays. A 30-day deadline might be only 22 working days. If your deadline is based on working days, subtract weekends and bank holidays from the calendar count.
Q: How do I calculate the number of weeks and days? A: Our weeks calculator does this directly. For example, 50 days = 7 weeks and 1 day. This is useful when planning in weeks rather than individual days.
Q: What if I need to know what day of the week a date is? A: We have a day-of-the-week calculator that shows which day any date falls on. Useful for checking if a deadline is a weekend, or for scheduling events.
Q: How do leap years affect day calculations? A: Leap years add an extra day (29 February instead of 28). This shifts the total by 1 day if your date range includes February in a leap year. The calculator accounts for this automatically, so you don't have to remember the leap year rule (every 4 years, except years divisible by 100, unless also divisible by 400).
Q: How do I calculate days remaining until a deadline? A: Subtract today's date from your deadline. Our calculator gives you this instantly. If you're tracking a big event or milestone, our countdown planning guide has more on managing multiple deadlines through the year.
Q: Can I use this for time tracking or project management? A: Yes. Once you know how many days (or working days) you have, you can break it into tasks and hours. The unit converter can help if you need to convert between days, hours, and other time units.