How date answers are calculated and interpreted.

Age in Days is a browser-first utility. This page explains the practical assumptions behind each mode so results can be interpreted with confidence, not treated as hidden policy outcomes.

Core model

All calculations use native browser date objects and a shared utility layer. Each mode builds a date range and then applies the mode-specific interpretation logic to display calendar days and derived totals.

Calendar assumptions

Dates are calendar dates, not time stamps.
Leap days are included through actual calendar rules.
Month breaks depend on calendar boundaries, not fixed 30-day blocks.

Reverse ranges

For two-date spans, the tool normalizes input order so the span can still be interpreted coherently. The returned total remains a numeric absolute span, while internal state tracks direction for narrative phrasing.

Working days

The working-day mode excludes Saturday and Sunday from the counted range. It does not apply region-specific holidays, office closures, or custom shifts automatically.

What changes between modes

Age mode focuses on elapsed age units.
Date span mode uses the same base range math with year/month/day decomposition.
Countdown mode labels targets before or after today differently.
Working days mode uses weekday filtering.

Why the method page exists

Users need a single place to verify assumptions, especially for edge cases. This page keeps the interpretation contract visible before deeper guide reading.