This free swim interval timer helps you train with clear timing and sound, without an app. It runs fully in your browser, so you need no account and no sign-up, and nothing you type leaves your device. Open it on a phone, tablet or laptop where you train, and it is ready in seconds.
A swim interval set uses a send-off time: the clock time at which each repetition starts, whatever your swim time is. If the send-off is 1:30 and you swim 1:12, you get 18 seconds of rest before the next rep starts. This tool works out that rest for you and totals the whole set, so you can plan a session before you get in the pool.
Set the number of repetitions, the send-off time in minutes and seconds, and your expected swim time, then press the start button to see the result. The tool shows rest per rep and the total session time. If your swim time is longer than the send-off, it warns you to pick a longer send-off, because that set cannot work as written.
Take a classic set: 10 repetitions of 100 metres on a 1:30 send-off, swum in about 1:12 each. That gives 18 seconds of rest per rep and a 15-minute set. Change the send-off to 1:20 and the rest drops to 8 seconds, which turns an aerobic set into a much harder one. Small send-off changes change the whole session.
The big display matters because training is physical. When you are out of breath, tired or mid-set, small text and quiet beeps fail. This tool uses a large clock, a clear phase label and a loud beep, so you can follow it from across a room or a pool deck without stopping to read.
Tip: Test the send-off on the first rep. If you finish with far more rest than planned, shorten the send-off next time; if you miss it, lengthen it.
Tip: Write the set on a board at the pool end. Swimmers forget send-offs mid-set, and a visible set keeps the lane together.
Tip: Keep the same send-off for the whole set. Changing it rep by rep makes rest random and the set hard to compare next week.
Common question: What is a good send-off? Pick one that leaves 10 to 20 seconds of rest for aerobic sets and 5 to 10 seconds for harder threshold sets.
Common question: Can I use it for any distance? Yes. The maths works for 50, 100, 200 metres or any distance, as long as you enter the right swim time.
Common question: Why does rest matter so much? Rest decides the training effect. More rest means faster swimming; less rest means endurance work. The same swim time trains differently at different send-offs.
The biggest mistake is picking a send-off from a faster swimmer. Your set should match your speed, not someone else's, or you will miss every send-off and swim tired.
This timer suits swimmers, swim coaches, triathletes and masters squads. It also suits anyone planning pool sessions who wants the maths done before the first dive.
On the day, charge the device the night before, open the tool early, and test the sound once before the session starts. A flat battery or a silent device in the first minute is an avoidable problem, and a one-minute test prevents it. Keep a charger nearby for long tournaments, and keep the screen bright enough to read in sunlight or under hall lights.
This tool is free to use as often as you like. Bookmark it, use it for every session, and share it with your training partners. A good timer does not make you fitter by itself, but it removes excuses, keeps sessions honest, and lets you compare this week with last week fairly.