Time calculators

These pages use the calendar on your computer. They do not call a server, and they do not drop statutory holidays.

Days between is end minus start in midnights. The start date is not included. A Monday to the next Monday is 7 days. Weekdays skip Saturday and Sunday and still count a holiday that falls on a weekday. A “10 business days excluding holidays” rule is stricter than this page. Add or subtract moves a start date by days, weeks, months, or years. Days and weeks are exact. Months and years keep the day of the month when it exists, and otherwise land on the last day of the month. 31 January 2026 plus one month is 28 February 2026, not 3 March. Thirty days is not the same instruction as one month.

Age counts birthdays up to the date you pick, then leftover months and days. A 29 February birthday is treated as 28 February in a common year. Due date adds 280 days to the first day of the last period, or 266 days to a conception date. From 15 January 2026 the last-period rule lands on 22 October 2026. An ultrasound date from a clinician replaces that estimate. The page is a planning sketch, not a diagnosis.