What is an interval timer?
An interval timer repeatedly counts a set number of seconds for "work" (or activity) and "rest." Unlike a stopwatch that times a single effort, it automatically handles the switch between motion and pause — for example, 45 seconds on and 15 seconds off, ten times. That makes it useful anywhere you want a rhythm: strength circuits, HIIT, run-walk running intervals, and even focus-and-micro-break study sessions.
How to use this timer
Opening this page loads ten rounds of 45 seconds of work plus 15 seconds of rest. Press Start and it cycles work-rest-work automatically while showing the rounds remaining. You can change the seconds and the number of rounds freely, and "Add timer" lets you build routines with three or more phases (for example work → rest → a different exercise). Copy the URL to save or share any setup, so you can bookmark your favorite routine.
Choosing your intervals
When in doubt, think in terms of the work-to-rest ratio. For harder efforts, use 2:1 (e.g., 40 seconds on, 20 off); for beginners or aerobic work, an even 1:1 (e.g., 30 and 30) is easier to handle. Set the number of rounds by working back from your total time — for a 10-minute session, that's a 60-second cycle times ten rounds. Start comfortable, then raise the load gradually by lengthening the work or trimming the rest.
Staying safe
For high-intensity work, always warm up with a few minutes of light movement before you start, and cool down afterward. Stop if you feel pain or strong dizziness, and sip water between rounds. If you have a medical condition or are just returning to exercise, keep the load light and consult a professional if needed.