Date Calculator
Calculate days between two dates, add or subtract days, weeks, months and years, count business days with US, UK, Canada, Australia and Germany public holidays, and run a live countdown. Timezone-proof civil-date arithmetic, entirely in your browser.
Result
Choose a start and end date to see the difference.
Difference between two dates
How these calculations are made
- • Dates are handled as civil year/month/day values and converted to a day number arithmetically, so no timezone offset or daylight-saving transition can shift a result.
- • Month and year steps clamp to the end of the target month: 31 Jan + 1 month = 28 Feb (29 Feb in a leap year), 29 Feb 2024 + 1 year = 28 Feb 2025.
- • The Include end date toggle governs the total-day count and the working-day count together, so the two figures can never disagree by one day.
- • Working days are Monday to Friday; selecting a holiday calendar also removes that country's nationwide public holidays, including observed days, and lists each one.
- • Week numbers follow ISO 8601 (weeks start Monday, week 1 contains the first Thursday), reported alongside the ISO week-numbering year.
- • Everything runs in your browser — no date you enter is sent anywhere.
About Date Calculator
The Date Calculator answers four distinct calendar questions from one page: how many days lie between two dates, what date falls a given number of days, weeks, months or years from a starting point, how many working days a period contains once weekends and public holidays are removed, and how long remains until an upcoming date. Every calculation is performed on civil dates — bare year/month/day triples converted to a day number — so results never shift with your timezone or a daylight-saving transition, and month arithmetic clamps to the end of the month instead of overflowing.
Why use a Date Calculator?
Most date calculators get the hard cases wrong. They parse YYYY-MM-DD as UTC midnight but read it back in local time, so users west of Greenwich see the previous day. They add days to a timestamp, so a spring-forward transition swallows a day. They call setMonth, so 31 January plus one month becomes 3 March. And they mix inclusive business-day counts with exclusive calendar-day counts in the same result panel, producing the classic off-by-one. This tool fixes all four: day arithmetic is integer arithmetic on a day number, month arithmetic clamps, and a single Include end date toggle governs the total-day count and the business-day count together.
Who is it for?
Project managers laying out milestones, lawyers and paralegals computing statutory notice periods and filing deadlines, HR and payroll staff measuring service length and leave entitlement, finance teams working to net-30 and net-60 terms, support teams tracking SLA clocks in business days across several jurisdictions, and anyone counting down to a launch, a contract renewal, a wedding or an exam.
How to use the tool
Pick a mode: Difference (days between two dates), Business days (working days, with optional public holidays), Add / subtract (date arithmetic), or Countdown (time remaining until a date).
In Difference mode, set the start and end date — use the Today buttons for a quick fill and Swap to reverse them; the order does not affect the result.
Decide how the end date should count with the Include end date toggle: off gives elapsed days (the usual choice), on counts both endpoints. The total-day and working-day figures always follow the same setting.
Read the headline total-day figure first, then the breakdown below it: years/months/days, weeks plus leftover days, hours, minutes, seconds, working days, and the weekday, ISO week and day-of-year for each date.
For working days, open the Business days tab, choose whether to count between two dates or add N business days to a date, and select a public-holiday calendar (United States, United Kingdom, Canada, Australia or Germany) — each skipped holiday is listed with its observed date.
For date arithmetic, open Add / subtract, enter a whole number and choose days, weeks, months, years or business days; month and year steps clamp to the end of the target month, so 31 January plus one month is 28 February (29 in a leap year).
For a live countdown, open Countdown, set the target date and copy the page link — it carries an ?until=YYYY-MM-DD parameter so anyone opening it sees the same countdown.
Use the Copy button on any headline answer to put the result on your clipboard, or Reset to clear the mode back to today's date.
Frequently Asked Questions
How do I calculate the number of days between two dates?
Open the Difference tab, set a start and an end date, and the total-day count appears immediately as the headline figure. The Include end date toggle decides whether the final day is counted: leave it off for elapsed days (7 September to 11 September 2026 is 4 days), switch it on when both endpoints belong to the period (5 days). Everything below the headline — years/months/days, weeks plus remainder, hours, minutes, seconds, working days, weekday names and ISO week numbers for both dates — recalculates from the same setting, so the calendar-day and business-day figures never contradict each other. The order you enter the dates in does not matter.
What is the difference between inclusive and exclusive date counting?
Exclusive counting measures the gap between two dates: subtract one from the other, and the end date is not part of the total. Inclusive counting treats both endpoints as part of the period, which adds exactly one day. Payroll periods, rental agreements, hospital stays, prison sentences and many court deadlines are inclusive; elapsed time and days-until calculations are exclusive. Neither convention is more correct, and the disagreement is precisely why two calculators can report 4 days and 5 days for the same pair of dates. This tool makes the choice explicit with a toggle and applies it to the total-day count and the working-day count at the same time.
Is this calculator private, and can my timezone change the result?
It runs entirely in your browser via JavaScript — the dates you type never reach a server and are never logged. Open DevTools' Network tab while you calculate: zero HTTP requests. Your timezone cannot change the result either. Dates are handled as civil year/month/day triples, and all day arithmetic runs on a day number computed arithmetically from the calendar, so no Date instant, no UTC offset and no daylight-saving transition is ever involved. Identical inputs produce identical output in Los Angeles, London and Kiritimati. The single exception is the Countdown ticker, which necessarily compares against your device's local clock.
Calendar days or business days — which should I use for a deadline?
Read the contract or statute; it will say which. Calendar days count every day including weekends and public holidays, while business days count Monday to Friday minus the holidays of a chosen jurisdiction. Court filing rules and statutory notice periods are usually business days; payment terms such as net 30 are almost always calendar days. The Business days tab counts working days between two dates or adds N working days to a date, using the United States (federal), United Kingdom (England and Wales), Canada (federal), Australia (national) or German calendar, and lists every holiday it removed. Observed days are handled: a US holiday on a Saturday shifts to the Friday before and on a Sunday to the Monday after, while UK, Canadian and Australian weekend holidays move to the next free weekday.
What happens when I add one month to 31 January?
You get 28 February, or 29 February in a leap year — the day is clamped to the last valid day of the target month. That is the convention calendar applications use and what people mean by a month later. JavaScript's built-in Date does something different: setMonth overflows, turning 31 January plus one month into 3 March, which is a frequent source of scheduling bugs. Year steps clamp the same way, so 29 February 2024 plus one year is 28 February 2025. Note that clamping is not reversible: 31 January plus one month minus one month lands on 28 January. When you need reversibility, add days rather than months.
Can I share a countdown to a launch date with my team?
Yes. The Countdown tab counts down to any date you choose and writes it into the page address as ?until=YYYY-MM-DD, so copying the URL — or using the Copy link button — gives colleagues the identical countdown when they open it. The ticker refreshes every second with the days, hours, minutes and seconds remaining until local midnight at the start of the target date, so a teammate in another timezone sees it reach zero at their own midnight rather than yours. Alongside the ticker the tool shows the plain calendar-day count, which is timezone-independent and is the figure to quote in a status report.
Why does the ISO week number not match the week number in my spreadsheet?
Because two incompatible systems are in use. ISO 8601 weeks start on Monday, and week 1 is the week containing the first Thursday of January — equivalently, the week containing 4 January. North American week numbering starts weeks on Sunday and calls the week containing 1 January week 1. Under ISO, 1 January 2027 (a Friday) is week 53 of week-numbering year 2026, not week 1 of 2027, whereas the default Excel WEEKNUM would report 1. This tool reports the ISO week together with the ISO week-numbering year, which is the only unambiguous way to write it. For standalone week lookups, see /tools/week-number-calculator/.
What are the tool's limits, and which calendar does it use?
It uses the proleptic Gregorian calendar with the standard leap rule — divisible by 4, except centuries not divisible by 400 — across years 0001 to 9999, so 1900 is correctly not a leap year while 2000 is. It does not model the 1582 Julian-to-Gregorian changeover, and it does not support the Hijri, Hebrew or Chinese calendars. Results are whole days: times of day, clock offsets and timezone conversions are out of scope. For a birthday-aware age see /tools/age-calculator/, for weekday lookups /tools/day-of-week-finder/, for epoch conversion /tools/epoch-converter/, for zone offsets /tools/timezone-comparison/ and for the leap-year rule itself /tools/leap-year-checker/.
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