How many calories do you burn in a hot tub?

So, how many calories do you burn in a hot tub? A little more than you would sitting on the sofa, but not many. One small study found an hour in water at 40°C (104°F) burned roughly the same as a half-hour walk, and much of that you would burn anyway. A hot tub is not a weight loss tool.

That does not make it pointless for your health. A warm soak can help you relax, ease stiff muscles and make it easier to keep up with exercise. Below we look at what the research actually shows, why the scale can mislead you, and how to use your tub safely alongside an active routine.

This article is general information, not medical advice.

How many calories do you burn in a hot tub?

Your body burns calories all the time just to keep you alive: breathing, pumping blood, repairing tissue and holding your temperature steady. Sitting still, an average adult burns very roughly one calorie (kcal) per kilogram of body weight per hour. Hot water nudges that figure up, but only modestly.

The best known research comes from a small study at Loughborough University, published in 2017 and led by Dr Steve Faulkner. Healthy men sat in a 40°C bath for an hour, and the researchers measured their energy use. They burned around 130 calories over that hour, roughly what the same people might burn on a brisk 30-minute walk.

It is worth reading that number carefully. The 130 calories is the total for the hour, not the extra. A person of similar size sitting quietly in a chair would burn a fair share of that anyway. The genuine extra from the heat is likely to be a few dozen calories at most.

For comparison, a person of about 68 kg (150 lb) burns roughly 50-70 calories an hour asleep and about 60-80 calories an hour watching TV. So a soak sits a little above your normal resting burn, not far above it.

Most people do not soak for an hour. If you scale the study figure down for a person of about 68 kg in water at 40°C, a 20-minute soak burns roughly 44 calories in total and a 30-minute soak roughly 65 calories. A typical home soak of 15-20 minutes gives about 35-50 calories, well below the headline number.

There are other limits too. The study was small, it used baths rather than hot tubs, and the volunteers stayed in for a full hour under supervision. That is longer than most manufacturers recommend for a soak at 40°C, so you should not try to copy it at home.

Why does sitting in hot water burn any extra calories?

When you sit in hot water, heat flows into your body instead of out of it. Your core temperature starts to climb, and your body works to bring it back down. That extra work costs a small amount of energy.

You can see some of this work happening. Flushed, pink skin and sweat on your face, neck and shoulders above the waterline are signs that your body is trying to shed heat.

What happens to your heart rate

To shed heat, your blood vessels near the skin widen so more warm blood can reach the surface. Your blood pressure tends to drop a little, and your heart beats faster to keep blood moving. This is why your pulse can feel quick after a long soak, even though you have not moved.

In hot water, heart rate typically rises by around 10-15 beats per minute, and more in hotter water or longer soaks. That is similar to the demand on your heart from a gentle walk.

A faster heart rate sounds like exercise, but it is not the same thing. During exercise your muscles are doing work and burning fuel. In a hot tub your muscles are mostly resting, so the overall energy cost stays low.

Almost all of the extra burn comes from your heart and your body's temperature control, with almost no muscle contraction. That is why soaking does not build strength, endurance or aerobic fitness, however often you do it.

Do you burn calories while sitting still in the water?

Yes, but most of what you burn is your normal resting burn. The heat adds a small layer on top. Sweating, a faster pulse and a slightly higher breathing rate all cost a little energy, but none of them come close to walking, cycling or swimming.

Your head and shoulders are usually above the water, so you also sweat from your face and neck. You can read more about this in our guide on whether you sweat in a hot tub.

Do body weight, temperature and soak time change the number?

All three make a difference, but none of them turn a hot tub into a workout. Think of them as small dials on a small number.

Body weight

A larger body burns more energy at rest than a smaller one, so a heavier person will burn a few more calories in the same soak. The extra from the heat itself is still small for everyone. Online calculators that give exact figures by weight are guessing, because no reliable data exists at that level of detail.

If you want a ballpark figure for planning, scaling the one-hour study figure by body weight gives these very rough hourly totals at 40°C. They are estimates, not measured values.

• 55 kg (120 lb): about 105 calories an hour
• 68 kg (150 lb): about 130 calories an hour
• 82 kg (180 lb): about 155 calories an hour
• 91 kg (200 lb): about 175 calories an hour

The same scaling gives these rough totals for the shorter soaks most people actually take at 40°C. Again, they are estimates, not measured values.

• 55 kg: about 35 calories in 20 minutes, about 52 in 30 minutes
• 68 kg: about 44 calories in 20 minutes, about 65 in 30 minutes
• 82 kg: about 52 calories in 20 minutes, about 78 in 30 minutes
• 91 kg: about 58 calories in 20 minutes, about 87 in 30 minutes

Water temperature

Hotter water raises your core temperature faster, which means a little more effort from your body to cool down. But the safe ceiling is 40°C (104°F), and you should not raise your tub above that to chase a few calories. Many people find 37-39°C (99-102°F) more comfortable for longer, gentler soaks.

Lowering the water from 40°C to about 38°C (100°F) cuts the calorie burn by very roughly 15-20%. In water barely above body temperature, around 37°C (99°F), your body has little heat to get rid of, so the burn stays close to resting levels.

Soak time

A longer soak burns more in total, simply because more time has passed. It also raises the risk of overheating, feeling faint and dehydration. For water at or near 40°C, many manufacturers suggest around 15-20 minutes at a time, though guidance varies, so check your manual.

Cooler water allows a longer soak. At 37-39°C (99-102°F), healthy adults can generally stay in for up to about 30 minutes, while at 40°C the usual limit is 15-20 minutes. Your manual may give different figures, and those come first.

At about 39°C (102°F), the usual limit sits between those two figures, at roughly 20-25 minutes. So the time allowed shortens step by step as the water gets hotter: about 30 minutes in cooler water, 20-25 minutes at 39°C and 15-20 minutes at 40°C.

That safe limit keeps the number modest. A 20-minute soak at 40°C burns roughly 35-58 calories depending on body weight, about the same as a small piece of fruit or a plain biscuit.

Why does the scale drop after a long soak?

If you step on the scales straight after a hot tub, you may weigh a little less. This is water, not fat. You lose fluid as sweat, and it comes straight back when you drink and eat.

The water around you hides the feeling of sweating, so it is easy to miss how much you lose. You can lose around 500-1,000 ml of fluid in a 30-minute soak without noticing, and get out already dehydrated.

On the scales, this usually shows as a drop of about 0.25-0.5 kg (half a pound to a pound) straight after a soak. It returns once you drink normally.

Fat loss happens slowly, over weeks, when you use more energy than you take in. A single soak cannot shift that balance in any meaningful way. Chasing a lower number on the scale with long, hot soaks only makes you dehydrated, which can leave you dizzy, tired and headachy.

To put it in numbers: even if all of the roughly 130 calories from a full hour came from fat, that would be only about 17 g of fat. In reality, not all of that energy comes from fat, so the true figure is lower.

If you track your weight, weigh yourself at the same time each day, before your soak, and after a normal amount of food and drink. That gives you a fair picture of your progress.

Hot tub, sauna, bath or shower: which burns more?

People often ask whether a sauna or a hot bath would be better for burning calories. The honest answer is that they all work in a similar way, by raising your body temperature, and they all give a small effect.

The table gives rough totals for 30 minutes for a person of about 68 kg (150 lb). They are estimates to show scale, not exact values.

The gap is clear. A brisk 30-minute walk burns about twice what a 30-minute soak does, and it also builds fitness.

Dry heat versus wet heat

Water carries heat into your body far more efficiently than air. That is why a sauna can be 70°C or more and still feel bearable, while water at 42°C quickly feels too hot. In both cases your body responds the same way, with sweating and a faster pulse.

Water transfers heat to your body roughly 25 times more efficiently than air. That is why a sauna at 70°C (158°F) or more and a hot tub at 40°C put a broadly similar heat stress on your body.

Traditional saunas typically run at about 65-90°C (150-195°F), far hotter than any hot tub. Yet because air carries heat so poorly, the rise in heart rate and the calorie burn end up broadly similar to a 40°C soak.

Because dry air raises your core temperature more slowly minute by minute, a sauna generally allows a longer session before the risks build up. Hot water can overheat you faster, which is why hot tub time limits are stricter.

There is no good evidence that one burns noticeably more than the other in normal use. Choose whichever you enjoy and will use safely.

Sauna calories and research

A 30-minute sauna burns roughly 40-75 calories for a person of about 68 kg, a similar range to a hot tub soak of the same length. A sauna visit, including breaks, often lasts 30-45 minutes in total, so the calories for a whole visit can end up level with or above a shorter hot tub soak.

By duration, rough estimates for a person of about 68 kg are about 25-35 calories in 15 minutes and about 90-130 calories in 60 minutes, including breaks. Per minute, that is slightly lower than a hot tub, but the longer sessions can even it out.

Some people rotate between a hot tub and a sauna for variety. It has been suggested that this may stop the body adapting to one type of heat, because adaptation can blunt the response over time, though the evidence for this is limited.

Sauna research is more extensive for heart health. A 2018 review linked regular sauna use to lower blood pressure, more flexible arteries and lower cardiovascular mortality. Hot water immersion, on the other hand, has the stronger direct evidence for effects on blood sugar. Neither replaces exercise or medical treatment.

For your goals, hot water immersion may give marginally better muscle recovery after exercise than a sauna, because the water also supports and warms your whole body evenly. A sauna suits people who prefer longer sessions and have access to dry heat. For calories, neither is a meaningful choice.

Hot baths and showers

A hot bath at up to 40°C works in much the same way as a hot tub, and it costs nothing extra if you already have a bath at home. A 30-minute bath each evening, at about 65 calories, adds up to roughly 400-450 extra calories over a week.

To compare with activity, a 20-minute hot bath at about 44 calories roughly equals a gentle 10-minute walk. A 30-minute bath at about 65 calories roughly equals 15 minutes of light cycling.

A 10-minute hot shower burns only about 10-20 calories. It is short, and the water runs over you rather than surrounding your body with heat, so your core temperature barely rises.

What about sauna suits?

Sauna suits are plastic or rubber garments worn during exercise to make you sweat more. They do not burn fat. They trap heat and stop sweat from cooling you, so you lose water quickly.

Sauna suits are popular in combat sports, where athletes use them to lose weight quickly before a weigh-in. The weight lost that way is fluid, not fat, and it returns once they drink. For ordinary fitness, the overheating risk is not worth it.

Any extra calorie burn is small. Sauna suits add only about 10-15% to the calories of a workout, and only when you actually exercise in them. Sitting still in one just makes you sweat and lose fluid.

That is a real risk. Without a way to cool down, your body can overheat, and heavy fluid loss can lead to heat exhaustion or heatstroke. Avoid them, and never wear anything similar in a hot tub.

Fluid losses of 2-3 litres in a single session are possible in a sauna suit. That can cause severe dehydration, stress on the kidneys, dangerous overheating and strain on the heart, and the risks are higher for people with existing health conditions.

Can a hot tub help with weight loss at all?

Not directly. Weight loss comes from your overall diet and activity over time, and the calories from a soak are too small to matter on their own. The NHS guidance on healthy weight focuses on eating well and moving more, not on heat.

Where a hot tub can help is indirectly. If a warm soak makes your body feel better after a run, a gym session or a long day of gardening, you may find it easier to stay active week after week. That consistency is what really counts.

How a soak compares with exercise

Activities that burn around 500 calories in 30 minutes, such as hard cycling, vigorous swimming, high intensity interval training (HIIT) or hard rowing for a heavier adult, burn about ten times what a hot tub soak does. Nothing safe burns 1,000 calories in 30 minutes, so be wary of any claim that it does.

Even elite athletes working at maximum effort burn only about 600-800 calories in 30 minutes. Claims of 1,000 calories in that time are usually based on fluid loss, or are simply inaccurate.

Everyday walking also beats soaking. 10,000 steps burns roughly 300-400 calories for a person of about 68 kg, spread over 80-100 minutes of walking. That is about two to three times what a full hour in a hot tub burns.

For most adults, 10,000 steps covers roughly 6.5-8 km (4-5 miles) at a pace of about 4.8-5.6 km/h (3-3.5 mph) on flat ground. Taller people with a longer stride cover a little more ground.

Cold exposure may also burn some calories by activating brown fat, a type of fat that produces heat. Research on this is still developing, and like heat, it is not a replacement for exercise.

Where it fits alongside exercise

• After exercise: warm water can ease stiffness and help you relax once your heart rate has settled.
• On rest days: gentle stretching in the water can keep you moving without strain.
• For sore joints: the buoyancy of water takes weight off knees and hips, which some people find makes light movement easier.
• For sleep: a soak earlier in the evening may help you wind down, and good sleep supports appetite control and recovery.

A hot tub raises your circulation and heart rate without putting any load on your joints. That makes it useful for people recovering from an injury or managing arthritis who want some gentle activity on a rest day. If you are under the care of a physiotherapist or doctor, ask them first.

Heat may also help recovery. When your blood vessels widen, circulation improves, which helps carry waste products away from muscles you have worked.

For sleep, timing matters. After a hot soak your core temperature drops, and that drop signals your body towards sleep. Soaking one to two hours before bed may help you fall asleep faster.

Our guide to hydrotherapy at home with your hot tub covers gentle movements you can try in the water. If you soak in the evening, see whether a hot tub before bed helps you sleep for timing tips.

Other effects of passive heating

Researchers are interested in passive heating for reasons beyond calories. The same Loughborough study reported that peak blood sugar after a meal was lower when volunteers had been in a hot bath. Other studies have looked at blood vessel health and inflammation.

Heat exposure may also trigger the release of heat shock proteins, which help protect cells under stress. Early research suggests regular heating could reduce markers of inflammation over time, but this evidence is preliminary.

These findings are early and mostly come from small groups of people under controlled conditions. They are interesting, but they do not replace exercise or medical treatment. For a wider look at what the evidence does and does not show, read our article on hot tub health benefits.

The NHS recommends adults aim for at least 150 minutes of moderate activity or 75 minutes of vigorous activity each week, plus strength exercises on two days. You can find the details on the NHS exercise pages. A hot tub does not count towards these targets, but it can sit happily alongside them.

How should you use your hot tub safely when you are getting fitter?

If you are using your hot tub as part of an active routine, a few simple habits will keep it safe and comfortable.

1. Let your heart rate and breathing settle after exercise before you get in. A cool-down walk and a few minutes of rest is enough for most people.
2. Drink about 500 ml of water around 30 minutes before you get in, and keep a bottle within reach while you are in the tub.
3. Check the water temperature on the control panel, and confirm it with a separate thermometer, because the panel reading is not always exact. Keep it at or below 40°C (104°F), and lower it if you plan a longer soak.
4. Keep your first soaks short, around 10-15 minutes, and build up slowly. Follow the time limits in your manufacturer's manual.
5. Sit with your shoulders out of the water now and then to let your body shed heat.
6. For a longer session, get out after 15-20 minutes, cool down for 10-15 minutes and drink some water, then get back in. Several short soaks are safer than one long one.
7. Get out slowly, holding a rail or the edge, because your blood pressure may drop as you stand.
8. Sit on the edge or a nearby seat for a minute before walking into a cold room or cold air. Going straight from hot water to cold air can cause rapid changes in blood pressure.
9. Within about 10 minutes of getting out, drink at least 500 ml of water or an electrolyte drink, and have a light snack if you exercised hard earlier.

Get out of the water straight away if you feel dizzy, sick, faint or confused, have a headache, or notice your heart racing or beating unevenly. Sit somewhere cool, sip water, and seek medical help if the symptoms do not settle quickly.

Common mistakes to avoid

• Turning the temperature above 40°C to try to burn more.
• Staying in for an hour to match a study done under supervision.
• Soaking straight after very hard exercise while still hot and breathless.
• Drinking alcohol before or during a soak, which adds to dehydration and the risk of fainting. Alcohol also widens blood vessels on its own, adding to the drop in blood pressure from the heat, and it is linked to drowning in hot tubs.
• Using the scale straight after a soak to judge fat loss.
• Skipping exercise because you have had a soak instead.

Keep your water clean as well. Sanitiser at the right level, usually 3-5 ppm free chlorine or bromine, and pH between 7.2 and 7.6, means you can soak comfortably without irritated skin or eyes.

When should you check with your GP first?

Hot water puts extra demand on your heart and changes your blood pressure. For most healthy adults that is fine in short soaks. Some people should speak to their GP, pharmacist or midwife before using a hot tub, especially alongside a new exercise plan.

• You have a heart condition, high or low blood pressure, or have had a stroke.
• You take medicines that can cause dizziness, drowsiness or low blood pressure.
• You take diuretics (water tablets), blood pressure tablets or blood thinners.
• You have had heat stroke or heat exhaustion in the past.
• You have diabetes, particularly if you have reduced feeling in your feet or legs.
• You are pregnant or trying for a baby. The NHS advises care with hot tubs and saunas in pregnancy because of the risk of overheating, so talk to your midwife.
• You have epilepsy or a history of fainting.
• You are starting a weight loss plan and have other health conditions.

Pregnancy needs particular care. Overheating in early pregnancy, especially the first trimester, is a concern for the baby's development, and many doctors and midwives advise avoiding hot tubs altogether. Ask your midwife before you soak.

Heat can affect blood sugar. If you have diabetes, you may need to check your levels before and after soaking, and your GP or diabetes nurse may advise adjusting when you take your medication around soaks.

If you are trying to lose weight for health reasons, your GP or practice nurse can help you plan safely. Many areas in the UK also offer free weight management support through the NHS.

Summary

Sitting in a hot tub burns slightly more calories than sitting still, because your body works to cool itself down. The extra is small, a few dozen calories at most in a normal soak, and any weight you lose straight afterwards is water.

Use your hot tub for what it does well: relaxing, easing stiff muscles and helping you recover. Pair it with regular exercise and a balanced diet, keep the water at 40°C or below, keep soaks short, and drink plenty of water.

Frequently asked questions

Is a hot tub after the gym a good idea?

It can be, as long as you let your body cool down first. Wait until your heart rate and breathing have settled, drink some water, then keep the soak short. Getting in while you are still hot from hard exercise raises the risk of overheating and feeling faint. Many people find a soak later in the day works better than one straight after training.

Does a hot tub burn belly fat?

No. You cannot burn fat from one part of the body by heating it, and a hot tub burns too few calories to reduce body fat anywhere. Fat loss depends on your overall diet and activity over weeks and months. A flatter feeling after a soak is usually down to relaxed muscles or fluid loss, which returns once you drink.

Which water exercises burn the most calories?

Water aerobics, lap swimming and pool running with a flotation belt burn roughly 400-700 calories an hour, depending on effort and body weight. That is far more than soaking. They need a cooler pool, not a hot tub. No exercise, in water or on land, can burn fat from just your belly, because the body loses fat from all over as a whole.

Is a hot tub better than doing nothing on a rest day?

In terms of calories, only slightly. The real value on a rest day is gentle movement and relaxation. Light stretching or slow leg movements in warm water can keep you mobile without strain. A short walk is still a better choice for burning energy, so consider doing both: a stroll in the afternoon and a short soak in the evening.

Can I swim or exercise in my hot tub to burn more?

Most hot tubs are too small and too warm for real exercise. Working hard in water at 38-40°C makes overheating much more likely. Gentle stretches and slow movements are fine, but save vigorous exercise for a cooler pool or dry land. If you want to exercise in water at home, a swim spa set to a lower temperature is designed for it.

Do cold plunges burn more calories than a hot tub?

Cold water also makes your body work to hold its temperature, mostly through shivering, so it can raise calorie burn briefly. As with heat, the effect is small and does not replace exercise. Cold water carries its own risks, including cold water shock, so start very gradually and speak to your GP first if you have a heart condition or high blood pressure.

Should I eat before using my hot tub?

Avoid a large meal just before a soak, because digestion and heat both draw blood away from the brain and can leave you drowsy or lightheaded. A light snack is fine, and can help if you exercised earlier and feel low on energy. Wait an hour or so after a big meal, and always drink water before and after.