Time Duration Calculator (Add & Subtract HH:MM:SS)
Add and subtract time durations in HH:MM:SS or MM:SS, one per line with optional + or −, and get the running total instantly — runs 100% in your browser with no upload.
2:00:30
🔒 Calculated in your browser — nothing is uploaded.
What this tool does
Paste or type a list of time durations — one per line — and this calculator adds them together and shows the running total in HH:MM:SS. Each line can be written as HH:MM:SS (for example 1:30:00) or as MM:SS (for example 45:30), and you can put a leading + or − in front of any line to add or subtract it. That makes it easy to answer questions like "how long were these five video clips altogether?" or "if I remove a 15-minute break from a 2-hour session, what's left?". The total updates the instant you type, and a secondary line shows the same result as a plain number of seconds so you can copy whichever form you need.
How the totals are calculated
Every line is converted to a signed number of seconds: hours are multiplied by 3600, minutes by 60, and seconds are added as-is, with a leading − flipping the whole line negative. The tool then sums all the lines. Field overflow is allowed, so 90:00 is read as 90 minutes (5400 seconds) rather than being rejected — handy when your source data isn't normalized. Blank lines and anything that can't be parsed are skipped and counted so you can spot typos. Because the math is a straightforward, deterministic conversion, the same list of durations always produces exactly the same total.
Frequently asked questions
How do I subtract a duration instead of adding it?
Put a minus sign in front of the line. For example, a list of 1:00:00 and -0:30:00 totals 0:30:00, because the second line is subtracted. A leading + is optional and simply means add.
What time formats are accepted?
Each line can be HH:MM:SS (like 2:05:30) or MM:SS (like 45:30), optionally starting with + or −. Fields may overflow, so 90:00 is treated as 90 minutes. Lines that don't match are ignored and reported so you can fix them.
Are the times I enter uploaded anywhere?
No. The durations you type never leave your device. Every calculation happens in your browser with JavaScript — nothing is uploaded, logged, or stored on any server.