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FIRST CH TOOLS / Misc / 56 BUSINESS DAY CALCULATOR

Business Day Calculator

Count how many business days (and calendar days) sit between two dates, or find the date that falls 14 business days from today or 10 business days after delivery — with weekends and Japanese public holidays taken out. It also turns a closing day and payment terms into the actual payment date, and you can add your own company holidays.

1 — WHAT TO CALCULATE

2 — WHICH DAYS ARE OFF

Add your own closures and working weekends

3 — DAYS AND BUSINESS DAYS

Nothing you type leaves the browser — every calculation runs on this page. Values can be passed in the URL: /en/date-calc/?start=2026-09-01&end=2026-09-30 / /en/date-calc/?mode=add&base=2026-09-20&n=10&unit=business / /en/date-calc/?mode=payment&invoice=2026-09-20&closing=eom&paymonths=1&payday=eom

How to Use

  1. Pick what to calculate“Between two dates” counts the days and business days in a range. “Start date + N days” gives you a delivery or acceptance deadline. “Closing day & payment terms” turns an invoice date into the day the money moves.
  2. Set which days are offWeekends plus Japanese public holidays are the default. Change the weekend, add the New Year break, list your summer shutdown, or mark the Saturdays your team actually works.
  3. Read it and copy itThe counts and the resulting date appear as numbers, with every holiday in the range (or every day that was skipped) listed underneath. “Copy” gives you a block to paste into an e-mail or a quote. Everything runs in the browser and nothing is uploaded.

About This Tool

A business day is any day that is not a weekend, a public holiday or a closure you listed. The holiday list is the one published by Japan's Cabinet Office, kept as-is, so the “Happy Monday” holidays that move each year (Coming of Age Day, Marine Day, Respect for the Aged Day, Sports Day), the substitute holidays that follow a Sunday holiday, and the citizens' holidays squeezed between two holidays (22 September 2026, for instance) are all in. Vernal and Autumnal Equinox Day, whose dates shift from year to year, come from the same list.

“N business days from today” is one step. Choose “Start date + N days” — the start date is already set to today — and type the number: 14, 25 or whatever the deadline says. The URL works the same way: /en/date-calc/?n=14&unit=business opens with the date 14 business days from today already worked out, and every skipped weekend and holiday listed.

The holidays in a range are counted too. “Between two dates” shows the number of public holidays next to the business days and calendar days, followed by the name and date of each one.

“Ten business days” differs by one depending on whether you count day zero. Japanese contracts that say “within 10 business days of receipt” normally start counting the day after receipt — the civil-code default, and the default here. If your agreement counts the day of receipt as day 1, tick “count the start date as day 1”. Which way you counted stays in the result table, so you can copy that line when you reconcile the date with the other side.

Payment terms resolve in two steps: closing day, then payment day. With “close at month end, pay at the end of the next month”, an invoice raised in September is closed on 30 September and paid on 31 October. When the payment day lands on a weekend or holiday, Japanese practice usually brings it forward to the previous business day, which is the default here; some contracts push it back instead. The result shows both the calendar days and the business days from the closing date, which is what a cash-flow check needs.

Your own days off can be added. List a summer shutdown, a founding anniversary or the New Year break (29 December – 3 January) and both the counts and the due dates avoid them. The other way round, a Saturday your team works goes in “extra working days” and counts as a business day. The weekend itself can be Saturday and Sunday, Sunday only, Friday and Saturday, or none at all.

Time zones cannot shift the answer. Internally every date is a plain integer — the number of days since 1 January 1970 — with no clock attached, so the result never moves by a day because of the device's time zone. The holiday list lives in a separate holidays.json and is replaced each year once the following year is published, around February; the years currently covered are printed under “which days are off”.

Related tools. To turn an agreed date into a calendar invitation use the ICS calendar event generator; for the difference between offices abroad use the time zone converter; to read epoch seconds out of a log use the Unix time converter.

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