Time Calculator

Use the Duration Math tab. Enter days, hours, minutes, seconds, and milliseconds in each row. Each row has a + or - toggle to add or subtract that duration. Click "Add Row" to include more durations, then press Calculate. The total is shown in all output formats including HH:MM:SS, Xd Xh Xm Xs, total seconds, and ISO 8601.

Use the Date Diff tab. Enter a start date/time and an end date/time using the date pickers. Press Calculate and the tool instantly shows total days, hours, minutes, seconds, and milliseconds. It also shows a human-readable breakdown ("X days, Y hours, Z minutes") and a weeks + days format. You can also use "Set Start = Now" or "Set End = Now" to anchor one side to the current moment.

ISO 8601 duration uses the pattern P[n]DT[n]H[n]M[n]S — where P starts the duration, D is days, T separates date and time parts, H is hours, M is minutes, and S is seconds. For example: 1 day, 2 hours, 30 minutes and 15 seconds = P1DT2H30M15S. This format is used in APIs, databases, and calendar systems (RFC 3339, Google Calendar, etc.).

Yes. There is no upper limit. You can enter 30 hours and the calculator correctly normalizes it to 1 day and 6 hours. You can also use the days field directly to handle multi-day durations. Calculations can span years — the tool handles any magnitude of duration correctly, including millisecond precision.

Use the Countdown tab. Pick a target date and time, optionally add a label, then click Start. If the target is in the future it shows a live countdown (time remaining). If the target is in the past it shows time elapsed since that moment — automatically switching to "elapsed" mode. The display ticks every second showing days, hours, minutes, and seconds.

After calculating, you can copy the result as: HH:MM:SS (standard time format), Xd Xh Xm Xs (human-readable), total seconds, total minutes, total milliseconds, or ISO 8601 duration (PT#H#M#S). Each format has its own copy button — click it and the value is instantly copied to your clipboard.

Yes, completely free. The Time Calculator runs 100% in your browser — no account required, no data sent to any server, no usage limits. Your calculation history is stored only in your browser's localStorage and never leaves your device. SnapUtils is ad-supported to keep all tools free and unlimited.