Day Counter — Days Between, Days Until
Days between two dates, the date N days from now, anniversary milestones, Japanese "within N days" deadlines counted under the Civil Code, and "N days before" deadlines counted backwards. Periods written in weeks are counted under art. 143(2).
How to use
Days between counts the days separating two dates — shown both as the plain difference and as an inclusive count (both ends included), which is what ticket windows and medication schedules usually mean.
Date after N days converts "90 days after release" or "30 days left" into an actual calendar date with its weekday.
Anniversary counter tells you what day you're on today, and lists the dates of upcoming milestones — day 100, day 1000, yearly anniversaries — so you can plan ahead.
Deadline (within N days) works out when a Japanese "within 14 days of the notice" clause actually expires. By default the start date is not counted (Civil Code art. 140), and a last day that falls on a weekend or a Japanese public holiday is moved forward to the next open day (art. 142). The result also shows day 1 and how far the last day was moved, so you can point at the numbers when the other side counts differently.
Deadline (N days before) handles the other direction — "at least 10 days before the auction", "two weeks before the shareholders' meeting". Counting starts from the day before the reference date, and the act itself must be done by the day before the last day, so "10 days before" really means 11 days before. If that last day is closed, the tool shows both the date it would move to and the date it would move back to, because the National Tax Agency circular that sets out this counting moves the two sides in opposite directions.
"Day N" vs "N days later" — the off-by-one trap
Calendar subtraction says Jan 1 → Jan 3 is 2 days, but anniversary culture counts the first day as day 1, making Jan 3 "day 3". In other words, day N = (N−1) days later. The anniversary mode defaults to the day-1 convention; untick the box for elapsed-days counting (start day = day 0).
How Japanese deadlines are counted
Under art. 140 of the Civil Code, when a period is expressed in days, weeks, months or years, the first day is not counted — unless the period starts exactly at midnight. A notice given on April 1 with a three-day limit therefore runs from April 2 and expires at the end of April 4 (art. 141). Art. 142 pushes the expiry to the following day when the last day is a Sunday or a public holiday and it is customary not to transact on that day. The statute only names the following day, so where a run of holidays follows, this tool does what practice does and moves on until an open day arrives. A date written into your contract or the entry rules of a competition overrides all of this, so follow that if there is one.
Periods written in weeks
Japanese statutes often set deadlines in weeks rather than days: a shareholders' meeting notice must go out "two weeks before" the meeting (Companies Act art. 299(1)). Article 143(2) of the Civil Code ends such a period on the day before the corresponding day of the final week, so the last day always falls on the same weekday as day one, however many weeks the period runs. Switch the unit selector to weeks to count that way.
Notes
- Leap years are handled automatically.
- For Feb 29 anniversaries, non-leap years roll the date to Mar 1 (following the browser's calendar rules).
- Public holidays are derived from the Holiday Act and are valid for 1980–2099 (the range of the equinox approximation).
- Need business days (skipping weekends and Japanese holidays)? Use the business days calculator.