Interval Running Timer

New to running? Start with 1 minute running, 1 minute 30 seconds walking, 8 times: 28 minutes 30 seconds in all

If you are just starting to run, jog for 1 minute and walk for 1 minute 30 seconds seven times, then finish with one more minute of running. Add 5 minutes of walking at each end and the whole session takes 28 minutes 30 seconds. This is week 1 of the NHS Couch to 5K plan, and it is already loaded when you open the timer above. Keep the same plan going for 9 weeks and by the last week you will be running 30 minutes without a break.

Press Start and the dot on the track travels one lap in the length of the current segment, while the big number inside counts down what is left of it. A rising tone tells you to run and a falling tone tells you to walk, so you never need to look at the screen to know what comes next. The workout profile below shows the whole session as bars of different heights, and the 9-week grid marks every run you have finished.

Why alternate running and walking

Interval running means swapping hard stretches with walking or slow jogging for recovery. If you cannot yet run for long without stopping, you can lengthen the running parts bit by bit. If you already run, breaking a fast pace into short pieces lets you hold it for longer in total than you could in one go. People mostly use this timer in situations like these.

• Starting to run: if even one minute of continuous running is hard, splitting running and walking is a realistic way in. The NHS plan begins with 1-minute runs in week 1, reaches a 20-minute run on the last session of week 5 and a 30-minute run in week 9.
• Coming back after a break: rather than jumping straight to 30 minutes at your old level, restart around weeks 4 to 5 and see whether your body keeps up. If you are recovering from an injury, talk to a clinician first.
• Building fitness or speed: in a study of four training methods, running 4 minutes hard four times (the 4×4) raised VO2max by 7.2% in 8 weeks, more than slow long-distance running did (Helgerud et al., 2007).
• Short on time: runners who trained with the 10-20-30 method cut their weekly running distance by more than half and still ran 5 km 48 seconds faster (Gunnarsson and Bangsbo, 2012). The main part takes 19 minutes with three blocks.
• Walking instead of running: older adults who alternated 3 minutes of slow walking with 3 minutes of fast walking gained leg strength and walking fitness (Nemoto et al., 2007). In Japan this is known as interval walking (インターバル速歩) and the study came out of Shinshu University.
• Hating to check the clock on a track or treadmill: the timer sounds each change and a 3·2·1 countdown just before it, so you do not have to keep looking at a watch.

How to use it

1. Pick a program: select a run in the 9-week grid, choose one of the three training presets, or enter your own run time, recovery time and number of sets under Custom. Editing a Custom field switches to that setup.
2. Warm-up, cool-down and countdown: choose 0, 3, 5 or 10 minutes for the warm-up and cool-down walks (5 is the default). The countdown before the start gives you time to tuck your phone into a pocket or armband, and it is not counted in the total time.
3. Check the sound: before you go, press Test sound to hear the rising and falling tones. Your phone's media volume affects the level too.
4. Start: the big number shows how much of the current segment is left, so the moment it hits 0:00 the next segment begins. The list on the right shows what comes next, and below it you see total time left, finish time and time spent running.
5. Pause, skip, reset: pausing freezes the clock and the scheduled sounds together. Skip jumps past the current segment, and the skipped time is taken out of your work time in the history. The program and times lock during a workout, so press Reset to change them.
6. Full screen: handy when the phone or tablet sits in front of a treadmill. Space starts and pauses, and in supporting browsers the screen is asked to stay awake while you train.
7. History and next run: finished workouts are kept in this browser, and the next run in the 9-week grid gets a dotted outline. It is loaded automatically the next time you open the page.

The 9-week plan (NHS Couch to 5K), run by run

Every run starts with 5 minutes of walking and ends with 5 minutes of walking, and the total time below includes those 10 minutes (stretching not counted). The NHS plan has you run three times a week for 9 weeks, with a rest day between runs. In weeks 1 to 4 and 7 to 9, all three runs of a week are the same.

Source: NHS Couch to 5K running plan (checked 19 October 2026); stretching time excluded.

Week 5 is the biggest hurdle. Within one week you go from three 5-minute runs to two 8-minute runs and then a 20-minute run, so the running time per session jumps. Up to week 4 the walking recovery is at least half as long as the running, but from the third run of week 5 you run with no walking break.

How much of the recommended weekly activity is three runs a week?

The WHO 2020 guidelines recommend that adults do 150 to 300 minutes of moderate-intensity aerobic activity a week, or 75 to 150 minutes of vigorous activity, and they count 1 minute of vigorous as 2 minutes of moderate. Vigorous means working at about 6 or more times your resting effort, with hard breathing, and running falls in that range unless it is so slow it is nearly walking. The table below counts only the running time as vigorous and leaves out the warm-up and cool-down walks.

From week 7 the running alone reaches the lower end of the vigorous target, 75 minutes a week. Before that, brisk walking in the warm-up and cool-down or extra walks on other days bring you closer. The guidelines also recommend muscle-strengthening activity on at least 2 days a week, separately from this.

Three training presets and the evidence behind them

Once you have finished the 9-week plan, or can already run 30 minutes without stopping, you can try intervals that have been tested in studies. Intensities and times copy each study's method, and warm-up and cool-down follow your timer settings (the totals below assume 5 minutes each).

The 10-20-30 study used 3 to 4 blocks; this preset uses 3 to suit people trying it for the first time. The method of alternating 30 seconds fast and 30 seconds slow (Billat et al., 2000) works in Custom if you enter 30 seconds of running and 30 seconds of recovery. In that study 8 distance runners averaged 19 repeats and stayed at VO2max longer than when running continuously at a pace halfway between lactate threshold and the speed at VO2max (7 min 51 s versus 2 min 42 s).

Intervals or steady running: which is better?

A meta-analysis of 28 studies with 723 healthy adults found that VO2max rose by an average of 5.5 mL/kg/min with interval training and 4.9 mL/kg/min with steady endurance training (Milanović et al., 2015). In the studies that compared the two methods head to head, intervals came out 1.2 ahead on average, but the authors rated the difference as possibly small. It is more accurate to see intervals as another way to get a similar benefit in less time than as a clear winner.

That is why many training plans fill most days with easy runs and add intervals only once or twice a week. Hard sessions such as 4×4 and 10-20-30 are best left until running feels familiar, and it is wise not to cram several of them into the same week.

Set the effort by heart rate and breathing

This timer only tracks time, so you have to choose the pace yourself. For presets defined as a percentage of maximum heart rate, such as 4×4, you can use an age-based estimate: 208 − 0.7 × age (Tanaka et al., 2001). At age 40, maximum heart rate is about 180 beats a minute, so the hard 4 minutes target 162 to 171 and the easy 3 minutes around 126. For other ages, use the heart rate zone calculator.

Without a heart rate monitor, judge effort by breathing. Moderate effort leaves you a little out of breath, and vigorous effort leaves you breathing hard. The runs in the 9-week plan should be a pace you can keep going to the end, not a sprint; only the 10 seconds in 10-20-30 and the 4 minutes in 4×4 should leave you really breathless. To check your pace against distance and time, use the running pace calculator.

How the total time is calculated

For Custom, total time is warm-up + run × sets + recovery × (sets − 1) + cool-down. Recovery only goes between runs, so there is one fewer than the number of sets, and after the last run you go straight into the cool-down. The examples below use 5 minutes each for warm-up and cool-down.

The countdown before the start is not part of the total time. The finish time is therefore the current time plus the countdown plus the total time, and it slides later by however long you pause.

How the sounds and the screen work

The tones for each change and the 3·2·1 countdown before it are all scheduled on the browser's audio clock the moment you press Start. Chrome wakes chained timers on a page that has been hidden for more than 5 minutes only once a minute, but sounds scheduled in advance are not affected, so they still play on time while you look at another tab. The time left is recalculated from the current clock each time, so you see the right value as soon as you come back.

Locking a phone screen can silence the sound, depending on the device and browser. To prevent that, the timer asks the screen to stay awake during a workout (the Screen Wake Lock API). The request holds only while the page is visible and is released when you switch to another app. Vibration works only in browsers that support it, such as Chrome on Android, and not in Safari on iPhone.

Staying safe

A study of exercise records from 4,846 people with coronary artery disease at three Norwegian cardiac rehabilitation centers found 2 cardiac arrests (both survived) in 46,364 hours of high-intensity interval training and 1 fatal cardiac arrest in 129,456 hours of moderate-intensity exercise (Rognmo et al., 2012). The authors concluded that the risk is low at both intensities, but those were supervised rehabilitation programs. If you have heart disease or high blood pressure, or have not exercised for a long time, check with a doctor before starting hard intervals.

• If you feel chest pain, dizziness or unusually severe breathlessness while running, pause and stop.
• Running near traffic or with earphones in can be dangerous. Keep the beeps at a volume that still lets you hear your surroundings, and run where the ground, lighting and obstacles are under control.
• On a treadmill, the timer does not change the belt speed. When a tone sounds, lower the speed with the buttons, and never jump off a moving belt.
• Use the screen only when you have stopped somewhere safe.

Common mistakes

• Running every run segment flat out: in the 9-week plan, run at a pace you can sustain to the end. If you gasp from the first segment, you will not finish the later ones.
• Assuming there is a recovery after every set: 8 sets of 1 minute running and 1 minute 30 seconds recovery include only 7 recoveries, so the session lasts 28 minutes 30 seconds, not 30.
• Running on consecutive days: the NHS plan is three runs a week with a rest day between. Skipping rest days to finish the 9 weeks sooner tends to overload your legs.
• Starting with 4×4 or 10-20-30: both studies used people who were already training. If you are new to running, finish the 9-week plan first.
• Skipping the warm-up walk: going straight into running makes the first segment unusually hard. Even if you are short on time, walk for at least 3 minutes first.
• Turning off the screen and waiting for the beep: sound can stop on a locked screen. Test it on your actual device before you head out.

Limits

• This timer measures time only. It does not measure distance, actual pace, heart rate or calories, and it cannot tell whether your effort is right.
• Distance-based intervals (for example repeated 400 m) have to be converted to time. If you run 400 m in 2 minutes, set the run to 2 minutes.
• Sounds may be late or stop when the screen is locked, in power-saving mode or while you use another app, and keeping the screen awake works only in browsers that support it.
• History stays in this browser only, so it does not follow you to other devices and disappears if you clear browser data.
• The intensities and times in the presets copy study methods and are not a personal exercise prescription. Results may differ if you are unlike the participants (trained men, moderately trained runners, adults in their 60s).

Sources

• 01NHS: Couch to 5K running plan9 weeks, 3 runs a week with a rest day between, run and walk structure and total time for each run (stretching excluded), 5-minute warm-up and cool-down walks
• 02Helgerud J et al. (2007), Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc 39(4)4 min at 90–95% HRmax × 4, 3 min at 70% between, 3 sessions a week for 8 weeks, VO2max up 7.2%
• 03Gunnarsson TP, Bangsbo J (2012), The 10-20-30 training concept improves performance and health profile in moderately trained runners. J Appl Physiol 113(1)30 s, 20 s, 10 s in 5-minute blocks, 3 to 4 blocks, 2 min between blocks, 7 weeks, distance down 54%, 5 km 48 s faster
• 04Nemoto K et al. (2007), Effects of high-intensity interval walking training on physical fitness and blood pressure in middle-aged and older people. Mayo Clin Proc 82(7)3 min slow (40%) and 3 min fast (over 70%), 5 or more sets, 4 or more days a week for 5 months, 246 people
• 05Milanović Z et al. (2015), Effectiveness of HIT and continuous endurance training for VO2max improvements. Sports Med 45(10)28 studies, 723 people, intervals +5.5 and endurance +4.9 mL/kg/min
• 06Rognmo Ø et al. (2012), Cardiovascular risk of high- versus moderate-intensity aerobic exercise in coronary heart disease patients. Circulation 126(12)4,846 people, 2 non-fatal cardiac arrests in 46,364 hours of high-intensity exercise and 1 fatal one in 129,456 hours of moderate
• 07Billat VL et al. (2000), Intermittent runs at the velocity associated with maximal oxygen uptake. Eur J Appl Physiol 81(3)30 s at vVO2max and 30 s at 50%, 19 repeats on average, 7 min 51 s at VO2max
• 08Tanaka H et al. (2001), Age-predicted maximal heart rate revisited. J Am Coll Cardiol 37(1)Maximum heart rate = 208 − 0.7 × age
• 09Bull FC et al. (2020), World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med 54(24)Adults: 150 to 300 minutes moderate or 75 to 150 minutes vigorous a week, muscle strengthening on 2 or more days
• 10Chrome for Developers: Heavy throttling of chained JS timers beginning in Chrome 88Chained timers on pages hidden for over 5 minutes run once a minute
• 11MDN: Screen Wake Lock APIAsks the screen not to dim or lock; the system releases it when the document is not visible
• 12MDN: Vibration APIWorks only on devices and browsers that support vibration

Frequently asked questions

Tools to use with it