Date & Time
Date and time tools cover calendar arithmetic (date differences, adding days, business days), clock-time duration and decimal-hour conversion, and fixed UTC offset conversion. Related tools such as the Date Difference Calculator, Add Days to Date and Business Days Calculator link together for common scheduling tasks.
Date Difference Calculator
Find calendar years, months, days and total days between two dates.
+DAYAdd Days to Date
Add or subtract a number of calendar days from a chosen date.
BIZBusiness Days Calculator
Count weekdays between two dates while excluding Saturdays and Sundays.
TIMETime Duration Calculator
Find elapsed hours and minutes between two clock times.
H→DHours & Minutes to Decimal
Convert hours and minutes into decimal hours.
D→HDecimal Hours to Time
Convert decimal hours into hours and minutes.
WEEKWeek Number Calculator
Find the ISO week number and ISO week-year for a date.
DOYDay of Year Calculator
Find a date’s ordinal day number within its year.
WORKWork Hours Calculator
Calculate paid work duration from start, end and unpaid break time.
UTCTime Zone Offset Converter
Convert a date and time between two fixed UTC offsets.
CDCountdown Timer
Count down live to a specific date and time.
POMOPomodoro Timer
Run a focus timer with work and break intervals.
What you will find in the Date and Time category
These tools handle the arithmetic of calendars and clocks. For calendar questions there are the Date Difference Calculator, the Add Days to Date tool, the Day of Year Calculator and the Week Number Calculator. For working time there are the Business Days Calculator, the Work Hours Calculator, the Time Duration Calculator and the two decimal-time converters, Decimal Hours to Time and Hours & Minutes to Decimal. For clocks across the world there is the Time Zone Offset Converter, and for managing attention and deadlines there are the Pomodoro Timer and the Countdown Timer. Together they cover most of the date and time questions that come up in planning, payroll, travel, study and project work, and each page shows its method and a worked example.
Calendar arithmetic that is easy to get wrong
Calendars are uneven. Months have 28 to 31 days, a leap year adds a day to February and a week can straddle two years. The date difference calculator reports both the calendar difference in years, months and days and the total number of days, which are two different answers to two different questions. The add days tool moves a date forward or back, so 45 days after 7 October 2026 is 21 November, and the day of year calculator tells you that 7 October is day 280. The week number calculator follows the ISO rule that week 1 contains the first Thursday, which is why 1 January can belong to the last week of the previous year. Using a tool removes the slips that creep into mental counting.
Working time, pay and schedules
Payroll and project planning depend on working time rather than calendar time. The business days calculator counts weekdays and leaves out Saturdays and Sundays, so ten business days is two calendar weeks, and you subtract any public holidays yourself. The work hours calculator subtracts unpaid breaks from the time between clock-in and clock-out, and the time duration calculator handles shifts that cross midnight. Timesheets often use decimal hours, so the two decimal converters change 7.75 into 7 hours 45 minutes and back. Remember that 0.5 hours is thirty minutes, not fifty, and that rounding rules vary by employer, so keep your own record of exact start and finish times.
Clocks, time zones and daylight saving
When people work across countries, the time zone offset converter turns a time in one fixed offset into another. Pakistan is UTC plus 5 all year, India is plus 5:30, and London and New York shift by an hour with daylight saving at different dates, which means the gap between two cities changes during the year. The converter uses the offsets that you enter, so choose the offset in force on the date of the event. Always write the date and the time zone when you share a time, because a late evening in one place can be the next day in another. For software, store times in UTC and convert only for display.
Focus, countdowns and deadlines
Two tools help you use time rather than just measure it. The Pomodoro timer alternates focused work with short breaks, usually 25 minutes of work and 5 of rest, and it makes a day of study or writing easier to plan in blocks. The countdown timer shows the days, hours and minutes left to a date, which turns a distant target into a set of weekly checkpoints. A countdown of 86 days, for example, is 12 weeks and 2 days. Combine the two with the date tools by working backward from a deadline: subtract the time that each stage needs, add a buffer and write the resulting dates in a calendar.
How days are counted in contracts and rules
Rules about deadlines differ in small but important ways. Some count the day of the event as day one and some begin the next day. Some use clear days, which exclude both the first and the last. Weekends and public holidays may or may not count, and a deadline that falls on a day off may move to the next working day or may not. Notices can run from the date of posting or from the date of receipt. The calculators give you the calendar answer, but you should read the exact wording of the contract, policy or law, and confirm the rule with the other party when the stakes are high.
Common mistakes
A few mistakes recur. People read 7.30 hours as 7 hours and 30 minutes when it means 7 hours and 18 minutes. They forget that 12:00 AM is midnight. They subtract times across midnight without adding a day. They ignore daylight saving when they schedule meetings. They use 30 days for a month when the contract means a calendar month. They add a week as 5 days when the count includes weekends. And they confuse the ISO week-year with the calendar year at the start of January. Each tool page lists the traps for its topic, and writing the rule you are applying beside the result is the best protection.
Tips, privacy and limits
Write dates in year-month-day form to avoid confusion between day-first and month-first formats, and keep a note of which counting rule you used. The tools do not know your country's public holidays, your employer's rounding policy or the daylight saving rules for a future year, so check those separately. All calculations happen in your browser, so the dates and times that you enter are not sent to Dekuz or stored. If you find a result that disagrees with an official calendar or a rule you rely on, please tell us through the contact page and we will check it.
Frequently asked questions about the date and time tools
Do the tools include public holidays? No, the business days calculator excludes Saturdays and Sundays only, so subtract holidays yourself. Why is my age in days different from years times 365? Leap years add extra days, and the exact count depends on the dates. Why does 1 January sometimes fall in week 52 or 53? The ISO rule gives week 1 to the week that contains the first Thursday of the year. Does the time zone converter handle daylight saving? It converts between the fixed offsets that you enter, so choose the offset in force on the date. Are my dates stored? No, everything is calculated in your browser, and nothing is sent to Dekuz.
A short glossary
A calendar day is any day, and a business day is a normal working day. A leap year has 366 days. UTC is the world reference time, and an offset is the difference from it. Daylight saving time moves clocks forward in summer in some countries. The ISO week starts on Monday, and week 1 contains the first Thursday. An ordinal date numbers the days of the year from 1. A decimal hour expresses minutes as a fraction of an hour. Elapsed time is the length of time between two moments, and a duration is the length of an interval. A timestamp marks a moment in time.
Getting started: a suggested path
Begin with the Date Difference Calculator and enter two dates that you know, for instance your birthday and today. Then try the Add Days to Date tool with a deadline, and the Business Days Calculator with a delivery window. If you track working time, use the Time Duration Calculator and the Work Hours Calculator for a typical day, and the decimal converters for your timesheet. If you work with people abroad, open the Time Zone Offset Converter for a meeting time. For focus and planning, use the Pomodoro Timer and the Countdown Timer. Each tool page has a worked example that you can reproduce.