Find the exact number of days, weeks, months and years between any two dates — in UK format.
Calculating the difference between two dates sounds simple, but date arithmetic involves several subtleties: varying month lengths, leap years, time zone considerations, and the question of whether you want calendar days or working days. This guide explains everything you need to know.
Under the hood, our calculator uses the JavaScript Date object. Every date in JavaScript is stored as the number of milliseconds since 1 January 1970 00:00:00 UTC — a value known as the Unix timestamp. To find the difference between two dates, you subtract one timestamp from the other and convert from milliseconds to days:
const diffMs = dateB - dateA;
const diffDays = Math.floor(diffMs / (1000 * 60 * 60 * 24));
This gives the total number of complete days between the two dates, correctly handling all leap years and month lengths automatically.
The United Kingdom uses the day-month-year format (DD/MM/YYYY), sometimes called the "little-endian" format. For example, 25 December 2025 is written as 25/12/2025. This differs from the American format (MM/DD/YYYY) and the ISO 8601 international standard (YYYY-MM-DD). When entering dates manually, always ensure you are using the correct format to avoid errors — our calculator's date picker enforces the correct locale.
The Gregorian calendar — used throughout the UK and most of the world since 1582 — inserts an extra day, 29 February, roughly every four years. The precise rule is:
This means a standard year has 365 days and a leap year has 366. Over a four-year cycle you average 365.2425 days per year. Our calculator handles this seamlessly — if your date range spans 29 February in a leap year, that day is counted automatically.
Many legal, financial, and employment situations require a count of working days rather than calendar days. In the UK, working days are Monday to Friday, excluding weekends and bank holidays. Common examples include:
Enter your date of birth and today's date to find your exact age in days. The average person lives approximately 29,200 days. A child born on 1 March 2020 has lived through one extra leap-year day (29 Feb 2020 was their first day, and 29 Feb 2024 adds another) — details your calculator handles automatically.
If a fixed-term contract runs from 1 April 2025 to 31 March 2026, the date difference calculator shows exactly 365 days (not a leap year). A contract from 1 March 2024 to 28 February 2025 spans 366 days because 2024 is a leap year.
UK statutory minimum notice is one week per year of service (up to 12 weeks for 12+ years). If you handed in notice on 14 February 2025 with a 28-day contractual notice period, the calculator instantly confirms your last working day as 14 March 2025.
A standard pregnancy lasts 280 days (40 weeks) from the first day of the last menstrual period. Enter that date and add 280 days to find your estimated due date. The date difference tool can also show how many weeks and days pregnant you are on any given date.
A personal loan taken out on 15 January 2025 with a 3-year term expires on 15 January 2028 — exactly 1,096 days (spanning one leap year, 2028). Interest calculations often use the exact day count.
A one-year warranty purchased 3 March 2024 expires 3 March 2025. A two-year extended warranty on the same item runs until 3 March 2026. Enter the purchase date and add your warranty length to confirm when cover ends.
One of the most popular searches: "how many days until Christmas?" Enter today's date as the start and 25/12/2025 as the end. As of 1 January 2025, there are exactly 358 days until Christmas Day 2025.
Our calculator also counts how many Fridays (or any specific weekday) fall between two dates. This is useful for payroll staff who need to know how many weekly pay days fall within a financial period, or for event planners scheduling recurring weekly meetings.
The Gregorian calendar was introduced by Pope Gregory XIII in October 1582 to correct the drift in the Julian calendar. Britain adopted it in September 1752, when 11 days were skipped (Wednesday 2 September 1752 was followed by Thursday 14 September). All modern date calculations use the proleptic Gregorian calendar for dates before 1752 in the UK, though historical accuracy varies.