Time Calculation Tools
Track hours, convert time zones, and measure durations with our free time calculation tools. From calculating hours worked on a timesheet to finding the time difference between cities, these calculators handle all your time arithmetic so you can focus on scheduling, productivity, and coordination across time zones.
Time Calculator
Add or subtract hours, minutes, and seconds to calculate time durations and differences.
Hours Calculator
Calculate the number of hours between two times for work tracking and time management.
Time Card Calculator
Calculate total work hours and pay from clock-in and clock-out times for weekly timesheets.
Time Zone Calculator
Convert times between any world time zones and find the current time anywhere.
Time Duration Calculator
Calculate the exact duration between two times in hours, minutes, and seconds.
Current Time Calculator
View the current time in any time zone around the world with live clock updates.
Time Difference Calculator
Calculate the time difference between two times or two time zones in hours and minutes.
Due Date Countdown Calculator
Count down the days, hours, and minutes until your due date or any important deadline.
How to Choose the Right Time Calculator
For general time arithmetic, the time calculator lets you add or subtract hours, minutes, and seconds in a single step, handling rollovers past midnight automatically. The time duration calculator is better suited when you have two specific times and need the elapsed duration between them, outputting the result in hours, minutes, and seconds.
If you are tracking work hours, the hours calculator gives you the total hours between a start and end time in both standard and decimal format. The time card calculator extends this with a full weekly timesheet, break deductions, overtime rules, and gross pay estimation, making it the right choice for payroll and employee time tracking.
For international scheduling, the time zone calculator converts any time to another time zone with daylight saving time adjustments. The current time calculator shows a live clock for any zone, and the time difference calculator tells you how many hours apart two zones or two specific times are. The due date countdown calculator is useful when you need a running countdown to a deadline, exam, or any future event.
Understanding Time Measurement and Time Zones
Time measurement is based on a system of 24 hours in a day, 60 minutes in an hour, and 60 seconds in a minute. This sexagesimal (base-60) system dates back to ancient Sumer and Babylon around 2000 BC. The choice of 60 as a base was practical: 60 is divisible by 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30, making fractional time calculations convenient long before decimal notation existed.
Coordinated Universal Time (UTC) is the primary time standard by which the world regulates clocks. UTC replaced Greenwich Mean Time (GMT) as the global reference in 1960 and is maintained by a network of atomic clocks. Time zones are defined as offsets from UTC, ranging from UTC-12 to UTC+14. Daylight Saving Time (DST) shifts the local clock forward by one hour during warmer months in participating regions, which means the UTC offset of a time zone can change twice a year.
Decimal hours express time as a single number rather than hours and minutes. For example, 1 hour and 30 minutes equals 1.5 decimal hours, and 2 hours and 15 minutes equals 2.25 decimal hours. Payroll systems, billing software, and project management tools frequently use decimal hours because they simplify multiplication by hourly rates. To convert minutes to decimal, divide by 60: 45 minutes equals 0.75 hours.
The International Date Line (IDL) runs roughly along the 180-degree meridian in the Pacific Ocean. Crossing the IDL westward advances the calendar by one day, and crossing it eastward sets the calendar back one day. This is why the first and last places to experience each new calendar day are both in the Pacific: Kiribati (UTC+14) sees the new day first, while Baker Island (UTC-12) sees it last, creating a 26-hour difference at the extremes.
Frequently Asked Questions
How do I calculate hours worked from clock-in and clock-out times?
Enter your start time and end time into the hours calculator or time card calculator. The tool subtracts the start from the end, accounting for AM/PM boundaries and overnight shifts. If you have a lunch break, enter the break duration and it will be deducted automatically. The result is shown in both hours-and-minutes format and decimal hours, which is useful for payroll calculations.
What is the difference between UTC and GMT?
UTC (Coordinated Universal Time) and GMT (Greenwich Mean Time) represent the same time in practice, but they differ in definition. GMT is a time zone based on the mean solar time at the Royal Observatory in Greenwich, England. UTC is a time standard maintained by atomic clocks and is not tied to any geographic location. UTC is the modern standard used by aviation, computing, and international communication. For most everyday purposes, UTC and GMT are interchangeable.
How do I convert between time zones?
Use the time zone calculator to select your source time zone and target time zone, then enter the time you want to convert. The calculator applies the UTC offset difference and adjusts for daylight saving time if applicable. For example, converting 3:00 PM Eastern Time (UTC-5) to Central European Time (UTC+1) means adding 6 hours, giving you 9:00 PM CET. During DST periods, offsets may shift by one hour.
What are decimal hours and why are they used?
Decimal hours express time as a single decimal number instead of separate hours and minutes. For example, 2 hours and 30 minutes is 2.5 decimal hours, and 1 hour and 45 minutes is 1.75 decimal hours. Payroll departments and billing systems use decimal hours because multiplying a decimal by an hourly rate is straightforward. To convert, divide the minutes by 60 and add to the whole hours.
How does daylight saving time affect time calculations?
Daylight saving time shifts the local clock forward by one hour in spring and back by one hour in fall. This means a time zone like US Eastern can be UTC-5 in winter (EST) and UTC-4 in summer (EDT). Time calculations that span a DST transition may gain or lose an hour. Our time zone calculator handles DST automatically, but if you are calculating manually, check whether a DST change occurs within your date range and adjust accordingly.