Guides

The conventions

Each guide covers one place where two careful people counting the same span get different answers because they read the question differently.

Seven days or eight? Inclusive and exclusive day counting

The gap and the count are different questions, and English has settled on rough conventions for which phrase means which. What "between", "through" and "within" usually intend, why the day of a triggering event is almost never counted, and why the last day always is.

What “within five business days” actually means

Courts, banks, carriers and employers each define a business day their own way. Court rules count every intervening day and protect only the landing day, banking rules separate a business day from a banking day, some carriers operate on Saturdays, and employers use their own office calendar. The guide also lists the four usual reasons your count differs from theirs.

Federal holidays and the observed-date rule

There are eleven federal holidays, and six of them are set by their position in the month. Why a holiday on a Saturday is observed on the Friday before, the one case where a deadline lands earlier than expected, and why federal offices, banks, markets and employers still close on different days.

Why two moon phase calendars disagree about the date

Two careful calendars can print the same full moon on different days, for three reasons: the 29.53-day shortcut, which drifts up to fourteen hours and is the only real mistake; the time zone a single instant lands in; and whether a phase is named by its instant or by an illumination band.

Underneath all of them

The method page sets out the rules for date arithmetic, federal holidays, moon phases and moon signs, and how the tests check them. Every answer on the site names the convention it used.