Date Difference

Calendar days count every day including weekends and holidays. This is the right unit for age, gestational duration, lease terms, and most legal deadlines (a '30-day notice' usually means 30 calendar days unless the contract specifies otherwise).

Business days exclude weekends. Use this for shipping estimates, payroll cutoffs, and project schedules. Standard US business days are Monday through Friday. Note that 'next business day' delivery from a Friday means Monday, not Saturday.

Working days exclude weekends and observed public holidays. The exact count depends on jurisdiction — the US has 10–11 federal holidays, the UK has 8 bank holidays, Germany has 9–13 depending on the state. This calculator's business-days mode skips weekends but doesn't subtract holidays; subtract those manually if your deadline depends on it.

Months don't have a fixed length. The difference between Jan 15 and Feb 15 is exactly 1 month, but it's also 31 days. The difference between Feb 15 and Mar 15 is also 1 month — but only 28 or 29 days. So 'months between two dates' is a slightly fuzzy quantity that can be expressed as either calendar months (counting month boundaries) or 30-day chunks. We report calendar months.

Year math has the same issue plus leap days. Someone born on Feb 29 only has a 'true' birthday once every 4 years; for legal purposes most jurisdictions roll their birthday to Feb 28 or Mar 1 in non-leap years. When calculating tenure or age in years, we count completed full years from the start date — the same convention used by HR systems and US legal age.

Tenure and anniversaries: hire date to today, in completed years and months. HR systems use this to calculate vacation accrual, vesting schedules, and service awards.

Project planning: kickoff date plus N business days = realistic delivery date that ignores weekends. Useful for SLAs, sprint planning, and contract milestones.

Notice periods and legal windows: lease termination, statute of limitations, appeal deadlines. Always check whether the relevant statute counts calendar days or business days — getting this wrong by a single day can be procedurally fatal.

Personal milestones: days since a quit date, weeks of pregnancy, time until a wedding or vacation. The 'countdown' use case is one of the most popular and a frequent reason people land on this page.