Is it still accurate if I turn off my screen or switch tabs?

Yes. The timer calculates elapsed time from real timestamps, so even if the browser is in the background and screen updates slow down, the actual phase transitions stay accurate.

How does the sound work?

There's no audio file — the alert tones are generated on the fly using the browser's Web Audio API, so there are no licensing concerns and it stays lightweight.

Does the session include a rest period after the last set?

No. The session ends as soon as the final set's work phase is complete — rest periods only occur between sets.

What happens if I close the browser tab?

Closing the tab resets the timer completely. To keep a session running, leave the tab open — switching to another tab or turning off your screen is fine.

Can I view the same timer on multiple devices at once?

No, the timer runs independently within each browser, so it doesn't sync across devices.

Is there a limit on the number of sets?

There's no hard cap, but setting too many sets at once makes for a very long session — we'd suggest staying within a realistic range (usually under 20 sets).

Interval Timer - Free Workout Set & Rest Timer

What is an interval timer?

Interval Timer is a tool that automatically calculates and runs the full timeline of a workout session based on the number of sets and your work and rest durations. It alerts you with sound and a color change every time the phase switches between work and rest, so you don't have to keep watching the screen. Timing is calculated from real timestamps, so it stays accurate even if your screen turns off or you switch to another tab. Many free web timers use a simple setInterval, which visibly drifts after just a few minutes in a background tab — this tool recalculates from timestamps instead, so it never drifts.

How to use it

Enter your number of sets, work time, and rest time (in seconds), then press "Start." When a work phase ends, it automatically switches to rest, then back to work for the next set, repeating all the way through the last set. You can pause at any time and pick up right where you left off with "Resume," or press "Reset" to set everything up again from scratch.

When it comes in handy

Keeping exact rest times between sets during weight training
Running interval workouts like circuit training or Tabata
Following along by sound during home workouts without staring at your phone
Reproducing a specific set/rest structure from a PT or group class

Why the timer stays accurate even with the screen off

A typical setInterval-based timer gets throttled once the browser tab goes into the background (most browsers do this to save battery), so after just a few minutes the displayed time can drift noticeably from real time. This tool instead recalculates the elapsed time — the gap between the start timestamp and the current timestamp — at every moment, so even if screen updates paused while you were on another tab, it snaps back to the exact correct point the instant you return.

Tips for interval training

Match rest time to intensity — high-intensity interval training (HIIT) typically uses a 1:1 or 2:1 work-to-rest ratio, while strength training benefits from longer rest (1:3 or more)
Well-known protocols like Tabata (20s work / 10s rest × 8 rounds) can be recreated exactly using this tool's set count and time inputs
If it's hard to tell phases apart by sound alone, the on-screen color change gives a visual cue too
If a rest period feels too short, you can always pause and resume whenever you need a moment

Frequently Asked Questions

Is it still accurate if I turn off my screen or switch tabs?: Yes. The timer calculates elapsed time from real timestamps, so even if the browser is in the background and screen updates slow down, the actual phase transitions stay accurate.
How does the sound work?: There's no audio file — the alert tones are generated on the fly using the browser's Web Audio API, so there are no licensing concerns and it stays lightweight.
Does the session include a rest period after the last set?: No. The session ends as soon as the final set's work phase is complete — rest periods only occur between sets.
What happens if I close the browser tab?: Closing the tab resets the timer completely. To keep a session running, leave the tab open — switching to another tab or turning off your screen is fine.
Can I view the same timer on multiple devices at once?: No, the timer runs independently within each browser, so it doesn't sync across devices.
Is there a limit on the number of sets?: There's no hard cap, but setting too many sets at once makes for a very long session — we'd suggest staying within a realistic range (usually under 20 sets).