This page documents the rules used by the calculators so you can understand exactly how a result is produced.
Calendar-Day Rule
Today is Day 0. One day from today is tomorrow. Standard day calculations count every calendar date, including Saturdays and Sundays.
Weeks
One week is treated as exactly seven calendar days. Adding whole weeks therefore preserves the weekday.
Calendar Months
Months are added as calendar months, not as 30-day estimates. When the starting day does not exist in the target month, the result is clamped to the final valid day of that month. For example, January 31 plus one month becomes February 28 or February 29 in a leap year.
Calendar Years and Leap Day
Years are added as calendar years. February 29 moved to a non-leap year is clamped to February 28.
Business-Day Rule
Business-day calculations advance only on the weekdays selected by the user. The default working week is Monday through Friday. Public holidays are not silently excluded because holiday calendars vary by location and institution.
Time Zone
The interactive calculator uses the visitor’s device date. Server-rendered fallback values use the WordPress site time zone until the browser updates supported dynamic result elements.
Validation Approach
Browser and server calculations are designed to use the same rules for days, weeks, months and years. Theme releases are syntax-checked and the packaged ZIP is validated before delivery. Important external deadlines should still be verified against the rule or authority that controls them.