Interval / HIIT Timer

How this calculation works

Each phase ends at a wall-clock time worked out when the phase begins, rather than after a counted number of ticks. That is what stops rounds drifting longer as a session goes on, which is the failure mode of every timer built by decrementing a counter. The tone changes pitch between work and rest, so you can hear which phase is starting without looking at the screen, and a longer tone marks the end of the session.

What the results mean

Round

Which repetition you are on. A round is one work phase plus the rest that follows it.

Total session

Work plus rest multiplied by the round count. Worth checking before you start, since interval sessions are usually longer than they look.

Phase tone

A higher tone starts work, a lower one starts rest, and a longer tone ends the session.

Common problems and fixes

The screen goes dark part way through

The device is dimming or locking because you have not touched it. Change the screen timeout in your system settings for the length of the session, or keep the device plugged in, since many devices use a longer timeout on power. A page cannot override a system screen lock.

Tones are late or missing

Press the test sound button once before starting, since browsers block audio until the page has been interacted with. If the tab is in the background when a phase changes, the sound is held until you return, so keep the tab visible during a session.

Frequently asked questions

More in Time

• StopwatchA stopwatch with laps that does not drift in a background tab.
• Countdown TimerA countdown that stays accurate when the tab is in the background.
• Pomodoro TimerFocus blocks and breaks, timed against the clock rather than counted.