Time Calculator

What this time calculator does

This English-language time calculator handles two common tasks: adding or subtracting durations (useful for timesheet math, estimating ETAs, or stacking task lengths), and computing the duration between two clock times (useful for counting hours worked or measuring a shift). Paste whatever format you have on hand — 01:30:00, 1h 30m, 90m, or bare seconds — and the forgiving parser figures it out. Results appear simultaneously as HH:MM:SS, a human-readable phrase, an ISO 8601 duration like PT1H30M, and total seconds, so you can copy the representation your API or spreadsheet expects. The Stack Overflow Developer Survey 2024 lists ISO 8601 as the most preferred date format among developers — this tool outputs it natively. 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs.

Features

• Forgiving input parser. Accepts HH:MM:SS, MM:SS, shorthand like 1h 30m 45s, or a plain integer treated as seconds. No reformatting required before you paste.
• Add or subtract mode. Chain two durations with a + or − operator to get a combined or remaining time — handy for calculating a clock-out time or merging two task estimates.
• Duration between two clock times. Enter a start and end time in 24-hour format to calculate elapsed time — ideal for work hours, meeting lengths, or shift duration.
• Four simultaneous output formats. Every result shows HH:MM:SS, a human phrase (e.g. '1 hour 30 minutes'), ISO 8601 (PT1H30M), and total seconds — cover all downstream needs in one shot.
• Time card and payroll ready. Add up multiple timesheet entries one at a time to get a running total. When you need to convert a Unix epoch, the [Unix timestamp converter](/en/timestamp-converter/) pairs well with this tool.
• No server, no data retention. All computation runs in your browser via JavaScript. Nothing is sent to any server, making this safe for internal work logs or sensitive project timelines.

How to use the time calculator

Choose a mode, type your values, and the result updates instantly — no button press needed.

1. Pick a mode. Select 'Add / subtract durations' to combine two time values, or 'Duration between two times' to measure the gap between a start and end clock time.
2. Enter your durations or times. Type in any format you have: 02:15:00, 2h 15m, 8100 (seconds), or MM:SS like 75:00. The parser normalizes all of them automatically.
3. Choose + or − (add/subtract mode). Toggle the operator between the two fields to add durations together or subtract one from the other. Results update in real time.
4. Copy the output format you need. Grab HH:MM:SS for a spreadsheet, PT2H15M for an API payload, or total seconds (e.g. 8100) to feed into a setTimeout or database column. For date-based math beyond durations, the [date calculator](/en/date-calculator/) covers adding days and months.

Common use cases

• Counting hours worked. Enter your clock-in and clock-out times (e.g. 09:00 to 17:30 in Chicago) to get exact hours worked. Add multiple shifts back-to-back to build a weekly timesheet total.
• Payroll and time card math. Many payroll systems require total minutes or decimal hours. Use the total-seconds output and divide by 3600, or copy HH:MM:SS directly into a time card calculator row.
• API and backend development. Convert a friendly duration like '1h 45m' to PT1H45M for ISO 8601 API fields, or to raw seconds for a Cache-Control: max-age header or a job scheduler interval.
• Estimating ETAs. Add a drive time and a cooking time to figure out when everything lands. Stack as many segments as you need by running the calculator multiple times with carry-over values.
• Meeting and project duration tracking. Record start and end timestamps from a calendar invite (e.g. 14:00–15:45 in America/New_York) to get an exact duration, then sum across meetings to see how much of your day was in calls.

Frequently asked questions