Decade calculator
Places a date in its decade, quarter and week. The decade question has a pedantic answer and a practical one, and they disagree by a year.
How to use the decade calculator
Strictly, decades run from year 1 to year 10; the 1990s would be 1991 to 2000, because the calendar has no year zero and counting starts at one. In practice nobody uses that: culturally the nineties are 1990 to 1999, defined by the shared leading digits, and that is how everyone refers to them. The strict version resurfaces only in arguments about when a century begins, which is why 1 January 2000 was celebrated as the millennium while the pedants pointed at 2001. Both are defensible; the digit-based one is what people mean, and it is the one this page uses — 1990 to 1999, as the span under the answer says.
Questions
Strictly 1991, because there is no year zero. Culturally 1990, and that is what people mean.
The system was devised before zero was in common use in European mathematics. Year 1 BC is followed directly by year 1 AD.
Strictly 1 January 2001. It was celebrated a year earlier because the digits rolled over.
A three-month block of the calendar year: Q1 is January to March.
Your device’s. The calculation runs in your browser, so it is today where you are rather than on a server somewhere else.