What this set is
A worked-out page for every day count people actually search for — one to thirty-one, then the round numbers and the administrative ones: 45, 60, 90, 120, 180, 365, 366 and on to five years. Each page gives the exact date, the weekday, the ISO week, the day of the year, the business-day equivalent, any US federal holiday inside the span, and whether the span crosses a clock change or a leap day.
The counts are not a range chosen to fill a list. They are administrative calendars: 7 and 14 are pay cycles, 28 is a prescription cycle, 30/60/90 are invoice terms and notice periods, 45 and 180 are the two deadlines in a section 1031 exchange, 90 is a probation period and a visa-waiver limit. Where a number has a real-world reason behind it, the page says what it is.
Two things worth knowing before you use one
Today is not day one. Every page here counts from tomorrow, which is the usual convention for a deadline expressed in days — and every page also shows the answer you would get if your rule counts today, because that off-by-one is the most common reason anyone checks a date twice.
Days are not months. 30 days from today and one calendar month from today are usually different dates, and 365 days is not always the same date next year. Both alternatives are linked from every page. If you want a start date other than today, use the date calculator.