About WhenMath

WhenMath exists because date and time questions are deceptively simple. "How many business days until this deadline," "what time is that meeting for me," and "how old will I be on that date" all sound like one-step arithmetic, right up until a weekend, a holiday, a leap year, a daylight-saving transition, or a month-end boundary changes the answer in a way a plain calculator never shows you. WhenMath's job is to give the direct answer and the reasoning behind it in the same place, so the assumption that produced a result is never hidden.

What WhenMath is not

WhenMath is not a scheduling app, a calendar you sync to, or a productivity suite. There is no account, no login, and nothing saved to a server. It is also not a legal, payroll, employment, tax, medical, or court-filing authority: a business-day count, a holiday preset, or an age calculation is calendrical arithmetic, not a determination that any specific employer, contract, agency, or jurisdiction is bound to follow. Where a result could be mistaken for that kind of authority, the page says so directly.

A system, not a directory

The site is organized into nine categories that group timing questions by the kind of reasoning they need (core clock arithmetic, calendar structure, working-day calendars, deadlines and capacity, timecards and shifts, recurrence, time zones, life dates, and active timers and daylight) rather than by search keyword. A tool only gets its own page on WhenMath when it solves a materially different problem from every other tool already on the site; a duration variant, a reversed direction, or a different unit is handled as a mode inside an existing tool, not a new page competing for the same intent.

How a result is built

Every calculation runs in your own browser. The inputs you type are read by JavaScript on the page, calculated there, and shown there; they are not sent to a server to produce a result. Where an assumption meaningfully affects the outcome, such as a counting convention or a holiday exclusion, the result states which one applied instead of leaving you to guess. See the Methodology page for the underlying calendar and time-zone rules, and Privacy for exactly what does and does not leave your device.

Where this is headed

WhenMath's tool set expands over time across the nine categories above, and each new tool is built and reviewed before it ships rather than published from a name alone. That is why some categories currently show an overview of the reasoning involved without a full set of tools underneath yet.