Whether you're counting down to a special event, calculating someone's exact age, or working out project timelines, date calculations are useful everyday tools. Understanding how to accurately count days between dates is essential for everything from legal deadlines to pregnancy tracking.
This guide explains how to calculate date differences accurately, including the impact of leap years, UK bank holidays for working day calculations, and common use cases from age verification to contract deadlines.
Common Date Calculations
| Use Case | What You Need |
|---|---|
| Age calculation | Years, months, days since birth |
| Countdown | Days until future date |
| Project planning | Working days between dates |
| Anniversary | Years/days since event |
| Pregnancy | Weeks since conception/LMP |
| Legal deadlines | Calendar or business days |
Example: Age Calculation
Birthday: 15 March 1990
Current date: 1 January 2025
Exact age: 34 years, 9 months, 17 days
Total days lived: 12,710 days
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Get instant results with our Date Calculator. Also check our Working Days Calculator and Age Calculator.
Days in Each Month
| Month | Days | Month | Days |
|---|---|---|---|
| January | 31 | July | 31 |
| February | 28/29 | August | 31 |
| March | 31 | September | 30 |
| April | 30 | October | 31 |
| May | 31 | November | 30 |
| June | 30 | December | 31 |
Quick Reference
- 1 week = 7 days
- 1 month = ~30.44 days (average)
- 1 year = 365 days (366 leap year)
- 1 decade = 3,652 or 3,653 days
Days Until Major Dates (From Jan 2025)
| Event | Date | Days |
|---|---|---|
| Valentine's Day | 14 Feb 2025 | 44 |
| Easter Sunday | 20 Apr 2025 | 109 |
| Christmas | 25 Dec 2025 | 358 |
| New Year 2026 | 1 Jan 2026 | 365 |
UK Bank Holidays 2025
When calculating working days, exclude these UK bank holidays:
| Holiday | 2025 Date | Day |
|---|---|---|
| New Year's Day | 1 January | Wednesday |
| Good Friday | 18 April | Friday |
| Easter Monday | 21 April | Monday |
| Early May Bank Holiday | 5 May | Monday |
| Spring Bank Holiday | 26 May | Monday |
| Summer Bank Holiday | 25 August | Monday |
| Christmas Day | 25 December | Thursday |
| Boxing Day | 26 December | Friday |
Note: Scotland has different bank holidays (2 January, St Andrew's Day). Northern Ireland includes St Patrick's Day and the Battle of the Boyne.
Working Days Calculation
For business and legal purposes, you often need working days (excluding weekends and bank holidays):
Calendar days - Weekend days - Bank holidays = Working days
Example: 1 January to 31 January 2025
31 calendar days - 8 weekend days - 1 bank holiday = 22 working days
Legal Notice Periods
Many UK legal requirements use specific day calculations:
| Requirement | Notice Period |
|---|---|
| Employment resignation | Typically 1-3 months |
| Landlord notice (periodic) | Minimum 2 months |
| Tenant notice | Typically 1 month |
| Consumer returns (online) | 14 calendar days |
| Parking fine appeal | 28 days |
| Council Tax appeal | 2 months |
Pregnancy Date Calculator
Pregnancy dates are calculated from the first day of your last menstrual period (LMP):
- Due date: LMP + 280 days (40 weeks)
- First trimester: Weeks 1-12
- Second trimester: Weeks 13-27
- Third trimester: Weeks 28-40
NHS dating scans at 8-14 weeks provide more accurate due dates based on fetal measurements.
Working Days vs Calendar Days: A UK Guide
Understanding the distinction between working days (also called business days) and calendar days is essential for legal deadlines, employment contracts, and financial transactions in the United Kingdom. Getting this wrong can mean missed deadlines, incorrect notice periods, or delayed payments.
Defining Working Days in the UK
A working day in the UK is generally defined as Monday to Friday, excluding public (bank) holidays. Saturday and Sunday are not considered working days for most legal and financial purposes, even if a business operates on those days. England and Wales observe 8 bank holidays per year, Scotland observes 9, and Northern Ireland observes 10. When calculating working day deadlines, each bank holiday within the period must be excluded.
Some contracts and legal contexts define working days differently. For example, certain financial regulations may define a business day as any day when the London Stock Exchange is open for trading. Always check the specific definition used in the document or regulation you are working with.
UK Employment Notice Periods
Notice periods in UK employment law are governed by the Employment Rights Act 1996 and typically run in calendar weeks, not working days. The statutory minimum notice periods are:
- Employee to employer: One week's notice, regardless of length of service (unless the contract specifies a longer period)
- Employer to employee: One week's notice for each complete year of continuous service, up to a maximum of 12 weeks. Employees with less than one month's service have no statutory right to notice.
Many employment contracts specify longer notice periods than the statutory minimum, commonly one month for junior roles and three to six months for senior positions. During the notice period, the employee remains entitled to their normal pay and benefits, including accruing annual leave. Garden leave, where the employee is asked not to attend work during the notice period but remains employed, is increasingly common in the UK, particularly in financial services and technology sectors.
HMRC Tax Year and Key Dates
The UK tax year runs from 6 April to 5 April the following year, a quirk dating back to the calendar reform of 1752 when Britain adopted the Gregorian calendar. Key dates every UK taxpayer should know include:
- 6 April: Start of the new tax year. New personal allowances, tax bands, and National Insurance thresholds take effect.
- 31 July: Deadline for second payment on account for Self Assessment taxpayers.
- 5 October: Deadline to register for Self Assessment if you are newly self-employed or have a new source of untaxed income.
- 31 October: Deadline for paper Self Assessment tax returns.
- 31 January: Deadline for online Self Assessment tax returns and payment of any tax owed for the previous tax year. Also the deadline for the first payment on account for the current tax year.
- 5 April: End of the tax year. Last day to use your annual ISA allowance, Capital Gains Tax annual exemption, and pension annual allowance for the current tax year.
Business Day Conventions in UK Finance
The UK financial sector follows specific business day conventions that determine how payment dates are adjusted when they fall on non-business days. The most common conventions are:
- Following business day: If the payment date falls on a non-business day, payment is made on the next business day. This is the most common convention for UK commercial loans.
- Modified following business day: Payment moves to the next business day unless it falls in the following month, in which case it moves to the preceding business day. This is standard for SONIA-linked derivatives and many international financial contracts.
- Preceding business day: Payment is made on the last business day before the scheduled date. Less common but used in some bond markets.
The TARGET2 calendar, used for euro-denominated payments, differs from the UK calendar and is relevant for businesses trading with European counterparts. Post-Brexit, UK and EU bank holiday calendars no longer align for certain financial operations.
UK Bank Holidays and Date Calculations
When calculating date differences for official or legal purposes, the eight standard bank holidays in England and Wales are: New Year's Day (1 January, or the following Monday if it falls on a weekend), Good Friday, Easter Monday, Early May Bank Holiday (first Monday in May), Spring Bank Holiday (last Monday in May), Summer Bank Holiday (last Monday in August), Christmas Day (25 December), and Boxing Day (26 December). When Christmas Day or Boxing Day falls on a weekend, substitute bank holidays are designated on the following weekday(s). Additional one-off bank holidays may be declared for special occasions, such as coronations or jubilees.
Frequently Asked Questions About Date Calculations
How do I calculate working days between two dates?
Count each Monday to Friday between the two dates, then subtract any bank holidays that fall within the period. Do not count the start date but do count the end date, unless the specific rule you are applying states otherwise. Our date difference calculator can perform this calculation automatically, accounting for all UK bank holidays.
What is the standard UK notice period for resigning from a job?
The statutory minimum is one week, but most contracts specify longer periods. One month is the most common contractual notice period for standard employment. Senior roles often require three months. Check your employment contract for the specific requirement, as the contractual period applies if it exceeds the statutory minimum.
Why does the UK tax year start on 6 April?
When Britain adopted the Gregorian calendar in 1752, eleven days were dropped to align with the European calendar. The Treasury refused to lose eleven days of tax revenue, so the tax year end date of 25 March (Lady Day, the traditional start of the English legal year) was moved forward by eleven days to 5 April. It has remained on this date ever since, making it one of the most enduring quirks of the British fiscal system.
Date Calculations in UK Law and Everyday Life
Date difference calculations play a surprisingly important role in UK legal, financial, and administrative contexts. UK contract law frequently requires precise date calculations for limitation periods, notice requirements, and statutory deadlines. Under the Limitation Act 1980, the standard limitation period for bringing a breach of contract claim in England and Wales is six years from the date of the breach, while personal injury claims must typically be brought within three years. Calculating these dates accurately, including accounting for leap years, is essential for both claimants and defendants.
In employment law, date calculations determine eligibility for various statutory rights. Employees must have two years of continuous service to qualify for unfair dismissal protection, calculated from the first day of employment to the effective date of termination. Continuous service is measured in complete calendar months, with each month running from the same date to the day before that date in the following month. Maternity leave calculations are similarly date-dependent: eligible employees can take up to 52 weeks of maternity leave, and Statutory Maternity Pay is available for 39 weeks. The qualifying week (the 15th week before the expected week of childbirth) must be calculated precisely to determine eligibility.
The UK tax year runs from 6 April to 5 April the following year, a quirk dating back to 1752 when Britain adopted the Gregorian calendar and the Treasury refused to lose 11 days of tax revenue. This non-standard start date means that calculating tax year boundaries requires specific attention. Similarly, the UK academic year typically runs from early September to late July, with term dates varying between England, Scotland, Wales, and Northern Ireland. School holiday dates affect everything from travel pricing to childcare arrangements, making date difference calculations practically useful for millions of UK families.
Practical Tips for Date Calculations in the UK
- Remember that UK dates use day-month-year format. The UK uses the DD/MM/YYYY format, which is the opposite of the US MM/DD/YYYY convention. This distinction is critical when reading legal documents, entering dates on international websites, or communicating with overseas colleagues. A date written as 03/04/2025 means 3 April 2025 in the UK but 4 March 2025 in the US. When ambiguity is possible, write the month name in full to avoid errors.
- Use the gov.uk holiday calendar for accurate working day counts. When calculating working days for business, legal, or employment purposes, always use the official gov.uk bank holiday list for the correct UK nation. England, Scotland, Wales, and Northern Ireland have different bank holidays, and using the wrong list can result in calculations that are off by one or two days.
- Account for leap years in long-term calculations. When calculating date differences spanning multiple years, remember that leap years add one extra day every four years (with century exceptions). Over a 10-year period, this adds two or three extra days to the total count. For financial calculations such as bond interest accruals or loan terms, even a single day's difference can have monetary implications.
- Know the key UK deadline dates by heart. Keep a mental note of critical annual dates: 31 January (Self Assessment tax deadline), 5 April (end of tax year), 31 July (second payment on account for Self Assessment), and the UCAS deadline of 15 January for most university courses. Having these dates readily available helps with quick mental calculations for planning purposes.
Additional Frequently Asked Questions
How do I calculate the exact number of days between two dates?
Why does the UK tax year start on 6 April?
How many days are there between Christmas and New Year?
Emma Thompson
Senior Content Editor
Emma is a senior content editor with a background in financial journalism. She specialises in making UK regulations and calculator tools understandable for consumers, working closely with qualified professionals to ensure accuracy.