Date Calculator

Count down to a date, calculate business days excluding weekends and holidays, or find the week number of any date.

Date Calculator

📐 How to Use

  1. Choose a mode: "Countdown", "Business Days", or "Week Number".
  2. Countdown: enter a target date to see the time remaining (or elapsed) in days, weeks, and months.
  3. Business Days: enter a start and end date, optionally add holiday dates (one per line) to exclude them from the count.
  4. Week Number: enter any date to see its ISO 8601 week number and year.
  5. Results update instantly as you type — no need to click Calculate.

🎯 When to Use This

  • Scheduling against a company calendar, where pasting your own public holidays into the box gives a working-day count that matches your office.
  • Reading the ISO week number for a production or sprint plan that labels periods as W32 rather than by calendar date.
  • Tracking how long is left before a filing deadline, with the countdown broken into days and hours as the date approaches.
  • Checking which Monday to Sunday range a particular date falls in, which the week number mode prints alongside the day of the year.

❓ Frequently Asked Questions

QHow is the countdown calculated?
The countdown takes the difference between the target date and right now, and shows it broken down into days, hours, weeks, and months. If the date is in the past, it shows how much time has elapsed instead.
QWhat counts as a business day?
By default, business days are Monday through Friday. Any dates you list in the holidays box (one per line, in YYYY-MM-DD format) are also excluded from the count, even if they fall on a weekday.
QWhat is an ISO week number?
The ISO 8601 standard divides the year into 52 or 53 numbered weeks, each starting on Monday. Week 1 is the week containing the year's first Thursday. This numbering is widely used in business, manufacturing, and government scheduling.
QCan week numbers go up to 53?
Yes — most years have 52 ISO weeks, but years where 1 January falls on a Thursday (or it's a leap year starting on Wednesday) have 53 weeks.
QIs my data sent to a server?
No. All date calculations happen locally in your browser using JavaScript. Nothing is sent to or stored on any server.

ℹ️ About This Calculator

ISO 8601 week numbering is the part of this that catches people out. Weeks run Monday to Sunday and week 1 is the week holding the year's first Thursday, so 1 January can land in week 52 or 53 of the previous ISO year. Business-day counting has a trap of its own: the answer depends on which end of the range you include.

Countdown compares your target date and time against the moment of calculation and reports the gap as totals and as a years, months, days and hours breakdown. Business days walks the range one day at a time and sorts each date into weekend, listed holiday or working day, with holidays entered one per line as YYYY-MM-DD. Week number returns the ISO week and ISO year, the day of the year, and the Monday to Sunday range containing the date.

⚠️ Notes & Limits

  • The countdown recalculates only when an input changes, so it is not a ticking clock and its figures drift until you edit a field or reload.
  • Holiday lines must be in YYYY-MM-DD form; anything else is skipped without warning, and a holiday on a weekend is counted as a weekend day instead.
  • Weekends are fixed to Saturday and Sunday, so a region with a Friday-Saturday weekend has to add those days to the holiday box by hand.
  • Week numbers follow ISO 8601 only. The US convention of Sunday-start weeks, with week 1 containing 1 January, produces different numbers and is not offered.

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