Date & Time Calculators

Which calculator answers which question

Minutes to decimal hours

Payroll, invoicing and timesheets are almost always kept in decimal hours, while clocks and rosters are kept in minutes. Seven hours and forty minutes is 7.67 hours, not 7.40 — a mistake that quietly costs money every pay period.

Decimal hours = hours + minutes ÷ 60

The time duration calculator returns both formats side by side, along with the total after breaks are deducted.

Calendar days, business days and the day you start counting

“Ten days from Friday” has at least three defensible answers, so the rule being applied matters more than the arithmetic:

• Calendar days — every day counts, weekends and holidays included.
• Business days — Monday to Friday only. Public holidays are excluded too, but which holidays depends entirely on the country and often the region.
• Inclusive vs exclusive counting — from the 1st to the 8th is 7 days if you count the gaps, 8 if you count the days themselves. Contracts, notice periods and hospital stays do not all use the same convention.

The date difference calculator reports calendar days, business days, weekend days and a field for custom excluded weekdays, so a Sunday-only week or a four-day schedule can be modelled directly instead of adjusted afterwards.

Timesheet rounding

Many employers round clock times to the nearest quarter hour. Under the widely used “7-minute rule”, minutes 1 to 7 round down and 8 to 14 round up, so a 9:08 start is recorded as 9:15 and a 9:07 start as 9:00. The practice is only defensible when it rounds in both directions over time — consistently rounding against the worker is not.

Why date arithmetic is harder than it looks

Months have no fixed length

“One month after 31 January” is undefined — there is no 31 February. Software resolves this differently: some clamp to 28 or 29 February, some roll forward to 2 or 3 March. Adding months then subtracting them is not guaranteed to return the original date, which is why the age calculator counts in whole years, then whole months, then remaining days rather than in a single unit.

Leap years are not simply every four years

A year is a leap year if it divides by 4, unless it divides by 100, unless it also divides by 400. 1900 was not a leap year; 2000 was. The next century exception is 2100.

A day is not always 24 hours

Where daylight saving applies, one day each year is 23 hours and another is 25. Durations crossing that boundary are off by an hour if computed as a plain subtraction of clock times — relevant for overnight shifts and anything billed hourly across a March or October weekend.

Weeks do not start on the same day everywhere

The ISO 8601 week begins on Monday and week 1 is the week containing the first Thursday of the year. The common US convention starts the week on Sunday. Two systems can therefore disagree by a full week number on the same date.

Reference: how long is a standard period?

Figures that come up constantly in planning, contracts and leave calculations, and that are quicker to look up than to derive.

A year contains 52 weeks and one spare day — two in a leap year — which is why a given date advances by one weekday each year and by two across a leap year. It is also why “52 weeks” and “12 months” are not the same period, and why a fortnightly pay schedule produces 26 payments in most years and 27 in some.

A pregnancy is dated as 280 days — 40 weeks — from the first day of the last menstrual period, not from conception, which is roughly two weeks later. The due date calculator applies that convention.

The formulas behind this category, and the published sources they come from, are listed on the methodology page.