Toolbox
A formula sheet plus reference tools for calculator, equation solver, units, elements, graphs and molecules.
Time and date calculator
Add days, hours and minutes to a moment to get the result across months and years, or measure the gap between two moments and check leap years.
Write moments as year-month-day hour:minute, for example 2026-10-24 08:00; a bare date counts as midnight.
- Start
- 2026-10-24 08:00
- Start weekday
- Saturday
- Crosses a month
- yes
- Crosses a year
- no
- 1Formula
Add the days to the date and carry the hours and minutes separately.
- 2Units
Bring both moments onto the same base of days and minutes.
- 3Solve
Repeat the same steps to reach the result.
- 4Check
Check whether the carry rolls into the next hour, day, month or year.
Concept
Dates cannot be counted in 30-day months: January, March, May, July, August, October and December have 31 days, April, June, September and November have 30, and February has 28 or 29.
A year is leap when it is divisible by 4 but not by 100, or when it is divisible by 400. So 2000 was leap and 1900 was not.
Going further
- Measuring a gap
- Convert both moments to one base, such as minutes since midnight of a fixed day, subtract, then split the total back into days, hours and minutes.
Common mistakes
- For a problem that crosses months, sketch a timeline with the key dates first.
- The number of days elapsed is a difference, while the day of the year is a position counted from January the first.