I built this interval timer because I couldn't find one that actually worked the way real training sessions work. Most online timers are basic, you set a work time and a rest time and that's it. But when you're running a group training session with pairs rotating between weights and cardio, or you're coaching team sport drills with specific exercise blocks and set counts, you need something that tracks the structure of the session, not just the clock. The Group 66 presets are built around exactly how I run sessions at REP66 — partner pairs alternating on a weight station and a cardio piece, across compound exercises and accessory work, with the timer telling both partners whose turn it is. It's free, no sign-up, no ads. Just a tool that works.

Select a preset from the list, or switch to the Custom tab to enter your own work time, rest time, and number of rounds. Hit Start — you'll get a 5-second get-ready countdown before the first interval begins. The timer counts down in seconds, turns red at 3 seconds remaining, and plays an audio cue when each phase changes. Use the Fullscreen button to expand the timer to fill your screen — ideal for projecting onto a TV during group classes or coaching sessions. The Volume slider goes all the way to 266% overdrive so the ding cuts through loud music. Use the Text Size slider to make the numbers readable from across a room. The gear icon opens the Settings panel where you can change colour themes, swap background images, and choose from 9 different audio packs.

Interval training is one of the most effective tools for improving cardiovascular fitness, and this timer handles it perfectly. For running, try the Cardio Blast preset — 30 seconds at hard effort, 15 seconds walking or slow jogging, repeated 10 times. That's a 7.5-minute block that will challenge even experienced runners. For cycling, AMRAP Blocks (40 seconds hard, 20 seconds easy, 6 rounds) matches well to most stationary bike programs. Use the Custom tab to build a classic 1:2 work-to-rest ratio — for example 20 seconds sprint, 40 seconds recovery — and adjust rounds to match your session length. The 3-second countdown beep gives you time to prepare for the next effort without watching the screen.

The Strength Sets preset is designed for traditional resistance training — 45 seconds of work followed by 75 seconds of rest, for 5 rounds. This suits exercises like dumbbell curls, lateral raises, or machine work where you want timed sets rather than counting reps. The longer rest period gives your muscles adequate recovery between hard sets. You can customise this completely in the Custom tab — many bodybuilders prefer 40 seconds on with 60–90 seconds rest. The timer removes the need to watch a clock between sets, so you can focus on the exercise, stay consistent with your rest periods, and avoid the habit of resting too long between sets which is one of the most common training mistakes.

Circuit training means moving from one exercise to the next with minimal rest, keeping your heart rate elevated across the whole session. AMRAP Blocks (40 seconds work, 20 seconds rest) is a classic circuit format — set up 6 stations, one round of the timer equals one full circuit. Cardio Blast (30 on, 15 rest, 10 rounds) suits a faster-moving circuit with lighter movements. Use the Custom tab to dial in your exact work-to-rest ratio, then use Fullscreen mode so the timer is visible to everyone in the room. The colour-coded display — red for work, green for rest — means participants can see the current phase at a glance without needing to read the text.

This timer was built with group training in mind. The fullscreen mode is designed to be projected on a TV or large screen so everyone in the session can see the countdown, the current phase, and the round number clearly. The audio cues mean participants can keep moving without watching the screen. For team sport coaching, use the Custom tab to build drill blocks — for example, 30 seconds of a specific movement drill followed by 15 seconds to reset and rotate, repeated for as many rounds as your drill requires. The text size slider lets you scale the numbers up so they're legible from the back of a room. The volume overdrive means the ding cuts through group noise and music without needing to connect to external speakers on maximum volume.

The Group 66 presets are built specifically for partner training. The idea is simple — one partner works at a weight station while the other does active recovery on a cardio piece, then they swap. Each 70-second work interval plus 30-second swap gives both partners a turn before moving to the next set. The timer displays exactly who is up on weights, which exercise you're on, and which set you're in — so there's no confusion, no one loses count, and the session runs itself. Choose 4 Compounds or 3 Compounds for your main lifts (3 sets each), then switch to 4 Accessories or 3 Accessories for isolation work (2 sets each). A full session of 3-compound plus 3-accessory work runs to approximately 50 minutes. It's an efficient, structured format that works whether you're training yourself and a mate, or running pairs in a group class.