A fortnight is fourteen days, and fortnight.now is built around that unit. See which fortnight of the year you are in, do the arithmetic on the fortnight calculator, generate fortnightly pay dates for the year, or count down to a date in fortnights. Free, and running in your browser.
Why fourteen days is a better unit than a month
A fortnight is a whole number of weeks, so it always begins and ends on the same weekday. Months do not, which is why anything recurring — pay, rent, sprints, bin collections, one-to-ones — so often runs fortnightly instead. The catch is that 26 fortnights make 364 days, so the cycle never quite fits a year, which is where the occasional 27th pay period comes from.
The vocabulary matters
"Biweekly" is genuinely ambiguous in American English, meaning either every two weeks or twice a week, and it is often confused with semimonthly, which is a different cycle entirely. "Fortnightly" has exactly one meaning, which is a good reason to prefer it in a contract.