Guides

The conventions

Every guide here covers one place where two careful people counting the same span get different answers. None of them is about arithmetic; all of them are about what the question meant.

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

A business day is not one thing. Courts count every intervening day and protect only the landing day; banking rules separate a business day from a banking day; carriers may operate Saturdays; employers use their own office calendar. Four readings, all correct, and the four reasons your count differs from theirs.

Federal holidays and the observed-date rule

Eleven holidays, six of them defined by position rather than date. 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

Three reasons, and only one is a mistake: the 29.53-day shortcut that drifts up to fourteen hours, the time zone a single instant lands in, and the difference between naming a phase by its instant and naming it by an illumination band.

Underneath all of them

The method page states every rule the calculators apply and how each is checked, and every answer on the site names the convention it used rather than picking one silently.