Date & Time Calculators
Count the days between two dates, work out working days around bank holidays, compare time zones, or find what day of the week a date falls on.
Which tool do I need?
This is the quickest way to the right one.
- How many days between these two dates?
- Date Calculator
- How many WORKING days, minus bank holidays?
- Business Days
- How long until a date I care about?
- Day Counter
- What day of the week was that?
- Day of the Week
- How old is someone, exactly?
- Age Calculator
- What time is it there right now?
- Time Zone Converter
- What time is it in several places at once?
- World Clock
- When do the clocks change?
- Daylight Saving Time
- What week number is this?
- Week Number
- What time is sunrise?
- Sunrise & Sunset
About Date and Time
Time zones and UTC
Coordinated Universal Time (UTC) is the world's primary time standard — all other time zones are expressed as UTC offsets (e.g. UTC+1 or UTC−5). Daylight saving time shifts the clock forward by one hour in summer, changing a region's UTC offset by 1. Not all countries observe DST — most of Asia, Africa, and China do not.
Calendar systems
The Gregorian calendar, in use since 1582, is the international standard. It has 365 days with a leap year every four years, except for century years not divisible by 400. ISO 8601 defines week numbering: weeks start on Monday, and week 1 is the week containing the year's first Thursday.
Date arithmetic
Calculating the days between two dates requires accounting for months of varying length and leap years. The cleanest technique converts both dates to Julian Day Numbers — integers from a fixed epoch — then subtracts. Business day calculations add the complication of excluding weekends and public holidays from the count.
Daylight saving time
DST shifts daylight into evening hours. Most of Europe switches on the last Sunday of March (forward 1 hour) and reverts on the last Sunday of October. The US follows the second Sunday of March and first Sunday of November. Because these dates differ, there is a brief window each year where the UTC offset between the US and UK differs from the usual gap.
Date and time questions
- Do the working-day tools know about bank holidays?
- Yes, and they derive them rather than reading a fixed list. Easter is computed with the anonymous Gregorian algorithm, the fixed dates carry the substitute-day rule that moves a holiday landing at a weekend to the next working day, and England & Wales, Scotland and Northern Ireland are handled separately because their holidays genuinely differ.
- Is the end date included when counting days?
- Each tool states which convention it uses, because both are legitimate and they differ by one. The Date Calculator reports the difference between two dates; the Business Days Calculator counts inclusively, which is what contracts and notice periods usually mean.
- How are time zones and daylight saving handled?
- From the IANA time zone database via your browser, so daylight saving transitions are applied automatically and correctly for each location — including the places whose rules differ from their neighbours. Nothing is hard-coded to a fixed offset.
- Do these work offline once loaded?
- Yes. All date arithmetic runs in your browser using your device clock and the built-in time zone data. Nothing is sent to a server, so nothing you enter leaves your device.