Which calculator should I use?
Match what you have to what you need.
| If you have... | Use... |
|---|---|
| A start time and an end time | Duration Calculator |
| A list of times to add together | Time Addition Calculator |
| A later time and want the earlier time | Time Subtraction Calculator |
| A time in 12-hour format you need in 24-hour format (or fractional hours) | Time Format Converter |
| A city name and want the current time in another city | Time Zone Converter |
| Clock-in and clock-out times for a shift | Work Hours Calculator |
Understanding the results: formats explained
Results appear in one of three formats.
HH:MM:SS, standard clock format. Example: 2 hours 30 minutes shows as 02:30:00.
Fractional hours, used for payroll and billing. Example: 2 hours 30 minutes shows as 2.50.
Total minutes, raw minute count. Example: 2 hours 30 minutes shows as 150 minutes.
The Duration Calculator and Work Hours Calculator show all three. The Time Addition and Subtraction calculators show only HH:MM:SS and fractional hours.
Why fractional hours appear in results
Payroll systems demand them. A timesheet that says "7 hours 45 minutes" must be entered as 7.75 hours to calculate pay.
Here is the conversion for the most common minute values:
| Minutes | Fractional hours |
|---|---|
| 15 | 0.25 |
| 30 | 0.50 |
| 45 | 0.75 |
| 5 | 0.08 |
| 10 | 0.17 |
| 20 | 0.33 |
| 40 | 0.67 |
| 55 | 0.92 |
Exact fractions: 1 minute is 0.0167 of an hour (1/60). 7 minutes is 0.1167 (7/60). 13 minutes is 0.2167 (13/60). 20 minutes is 0.3333 (20/60). 40 minutes is 0.6667 (40/60). 45 minutes is 0.7500 (45/60). The calculator rounds to four places for precision.
How the time zone converter handles DST
The Time Zone Converter uses the IANA time zone database. It applies the DST rules for the selected city on the selected date automatically.
This means:
- Compare London and New York in March. The US switches earlier than the UK. The difference shows 4 hours or 5 hours depending on the exact date.
- Compare Phoenix and Denver in July. Arizona does not observe DST. The difference is 1 hour in summer, 0 hours in winter.
- The converter never asks "is DST active?" It reads the date and the city's rules.
Rules change. The US Sunshine Protection Act (proposed permanent DST) passed the Senate in 2022 but stalled in the House. It was reintroduced in 2023, 2024, and 2025. The EU proposed ending clock changes in 2019 but remains deadlocked. The database is updated when changes are enacted. The calculator uses the version current on 30 September 2026.
Why does my time calculator result look wrong?
"I entered 14:00 and got an error." The Duration Calculator expects 12-hour format with AM/PM, or 24-hour format. 14:00 reads as 2:00 PM. If you mean 2:00 AM, type 02:00.
"The result is negative." You entered an end time earlier than the start time. For a shift that crosses midnight (22:00 to 06:00), add 24 hours mentally or use the Work Hours Calculator. It handles overnight shifts.
"The fractional hours look wrong." Confirm you are reading the fractional column, not the HH:MM column. 1.50 is one and a half hours (1 hour 30 minutes), not 1 hour 50 minutes.
"The time zone shows the wrong offset." Check the date. The converter shows the offset for the date you entered, not today's offset. Planning a meeting in March 2027? The offset may differ from today's.
Browser time vs server time
The time zone converter and current-time displays use your browser's local time. No location permission is requested. The calculator reads the time zone your operating system reports. If your system clock is wrong, the results will be wrong.
Most browsers synchronise with internet time servers automatically. If you suspect a mismatch, check your computer's date and time settings before relying on the converter for a critical meeting.