Date Difference Calculator
Two tools in one: find the difference between two dates (with business days), or calculate a future or past date by adding or subtracting calendar days.
Reviewed by Richard Ross · Last updated April 2026
How Date Difference Calculator works
Calendar days vs business days
Calendar days count every day from start to end, including weekends and public holidays. Business days (also called working days) count only Monday to Friday. For payroll, legal deadlines, and contract timelines, business days matter. This calculator counts weekdays only — it does not exclude UK public holidays, so adjust manually for bank holiday periods.
How years, months, and days are calculated
The years, months, and days breakdown counts the difference in the same way as age: complete years first, then complete months, then remaining days. The total days figure is calculated directly from the date timestamps and is always exact. The years/months/days breakdown is a human-readable approximation because months have different lengths.
Common uses
Date difference calculations are used in contracts and legal deadlines (when is 90 days from today?), project planning (how many working days until the deadline?), financial settlements (value dates, payment terms), and everyday curiosity (how long ago was a birthday or event?). The business days count is especially useful for supply chain and financial applications.
Negative differences and date ordering
This calculator always returns a positive result by treating the earlier date as the start and the later date as the end, regardless of which you enter first. If you need to know how far in the future a date is, the result is the same as how far in the past it would be — the direction is inferred from context.
Frequently asked questions
How many days are in a year?
A standard calendar year has 365 days. A leap year (any year divisible by 4, except century years not divisible by 400) has 366 days. On average over a 400-year Gregorian calendar cycle, a year has 365.2425 days. For date difference calculations, exact day counts are used rather than average years.
Does this calculator include public holidays?
No — the business days count excludes weekends only. It does not exclude UK bank holidays. For legal or contractual deadlines, check whether public holidays are excluded from the definition of "business days" in your specific context.
How many weeks are in a year?
A year has 52 complete weeks plus 1 day (or 2 in a leap year), giving 52.18 weeks on average. For practical purposes, most annual calculations use 52 weeks, and monthly calculations use 4.33 weeks per month.
What is the difference between calendar days and working days?
Calendar days include every day of the week, including weekends and holidays. Working days (business days) typically refer to Monday through Friday, excluding public holidays. For 5-day delivery estimates, legal 30-day deadlines, or payment terms, confirm whether the terms refer to calendar days or working days.
How do different countries define working days?
Working day conventions vary significantly. In the UK, standard working days are Monday-Friday excluding bank holidays (8-9 per year in England and Wales). Scotland and Northern Ireland have different bank holidays. The EU Working Time Directive (which still shapes UK employment law post-Brexit) limits working weeks to 48 hours on average. Some industries and contracts define working days differently — always check the specific definition when using date calculations for legal or contractual deadlines.
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