Workout Interval Timer

Why interval timing changes the workout

Interval training works by alternating hard effort with measured recovery on a fixed clock, so the structure of the session — not your willpower or a vague sense of "enough" — decides when you push and when you rest. That structure is what this timer enforces. You build a plan of exercises, each with a work duration, a rest duration, and a number of rounds, and the tool expands it into a precise second-by-second sequence with audible cues so you never have to glance at your phone mid-rep. The large countdown ring changes colour by phase: blue during work, green during rest, purple when the whole workout is done.

The three formats, and how this tool models them

The built-in presets encode exactly this. The Tabata preset is two exercises at 20/10 for 8 rounds. The EMOM preset uses 20s work + 40s rest so each round is precisely one minute — the defining feature of "every minute on the minute." The AMRAP preset is a single 420-second (7-minute) block with no rest and one round, because in AMRAP the clock simply runs down while you keep moving.

How the sequence is built — a worked example

Say your plan is one exercise: Burpees, work 30, rest 15, rounds 3. The tool flattens this into a list of segments before the timer starts: work 30 → rest 15 → work 30 → rest 15 → work 30 → rest 15. The total is calculated as rounds × (work + rest) = 3 × (30 + 15) = 135 seconds, shown live in the builder. Add a second exercise and its segments are appended to the same continuous sequence, so a circuit of several exercises plays end to end without you touching anything. Note that a rest segment is only inserted when rest is greater than zero — set rest to 0 and the rounds run back to back, which is how the AMRAP block stays unbroken.

How the audio cues work

Every tone is generated on the fly with the Web Audio API — the tool creates oscillators at specific frequencies rather than downloading sound files, so the cues work even with no network connection and add nothing to page weight. The cues are deliberately distinct so you can react without looking:

• Two high beeps (880 Hz) mark the start of a work interval.
• One lower beep (440 Hz) marks the start of a rest interval.
• A short tick (1100 Hz) fires on each of the final three seconds of any segment, counting you down to the switch.
• Three chimes (660 Hz) signal that the entire workout is complete.

Because browsers block audio until you interact with the page, the sound engine wakes up when you press Start. If the first session is silent, that interaction requirement is usually why; starting the workout once fixes it.

Practical tips

• Save the plans you repeat. The Save Plan button writes your current exercise list to the browser's local storage, and Load Plan brings it back on your next visit. Build your Monday circuit once and reload it weekly rather than re-entering it.
• Use the per-row duration readout to balance a circuit. Each exercise row shows its own total time, so you can see at a glance that a 5-round block dwarfs a 2-round one and adjust before you start.
• Keep the screen awake. The countdown is visual as well as audible; on a phone, prevent the display from sleeping mid-set so you can check the ring during a hard interval.

Common mistakes

• Setting rest to zero by accident. With rest at 0 the tool runs every round of work continuously with no recovery — fine for an AMRAP grind, brutal if you meant a 20/10 Tabata. Double-check the rest column before you start.
• Building an EMOM that doesn't sum to 60. EMOM only behaves like a true minute-based interval if work plus rest equals 60 seconds. Set 25s work and 35s rest, not 25 and 30, or your "minutes" will drift.
• Trusting the timer to scale your effort. A timer controls duration, not intensity. Tabata only delivers its benefit if the 20 seconds are genuinely maximal; an easy 20 seconds is just a slow interval. The clock keeps you honest on time, but the effort is yours.