Quick Answer: A hot tub burns calories, but not many — a Loughborough University study led by Dr. Steve Faulkner found one hour of passive hot water immersion burns roughly 140 calories, comparable to a 30-minute walk. That’s real but modest energy expenditure driven by your body working to cool itself, not a fat-burning effect of the water. Used consistently alongside diet and exercise, a hot tub is a reasonable recovery and relaxation habit — it is not a weight-loss method on its own, and any scale drop right after a soak is water weight, not fat.
Hot tub retailers and wellness blogs love the phrase “soak your way slim.” Here’s what the actual research measured, what it doesn’t support, and how to think about a hot tub’s real role if weight loss is part of your goal.
The numbers behind the “hot tub diet” claim
- ~140 calories is what Dr. Steve Faulkner’s team at Loughborough University measured for one hour of passive immersion in water around 104°F — the study most “hot tub burns calories” claims trace back to.
- That 140-calorie figure is roughly equivalent to a 30-minute walk, according to the same research — a real but modest number next to the 300-600+ calories an hour of moderate cardio typically burns.
- Passive heating raises core body temperature, and the body’s cooling response (increased heart rate, dilated blood vessels, sweating) is what drives the calorie burn — the same general mechanism mild exercise uses to raise metabolic rate, just at a much lower intensity.
- A broader body of research on repeated passive heat therapy has looked at cardiometabolic markers like blood sugar and vascular function, with some promising early signals — but reviewers note study protocols and populations vary too much to call the evidence strong, and none of it supports meaningful fat loss from soaking alone.
What a hot tub can’t do
The 140-calorie number sounds appealing until you compare it to what it’s being sold to replace. A 30-minute run, cycling session, or strength workout burns several times more energy than an hour in a hot tub — and unlike a soak, exercise also builds the muscle mass that raises your resting metabolic rate long-term. A hot tub has no equivalent effect on muscle or long-term metabolism; the calorie burn stops the moment you get out. Marketing that frames a hot tub as a stand-in for a workout is overselling a real but small physiological effect.
There’s also a common trick worth naming directly: stepping out of a hot tub and onto a scale often shows a lower number, but that’s sweat-driven water loss, not fat loss. Rehydrate — which you should, since hot water immersion is genuinely dehydrating — and the number returns within hours.
Where a hot tub actually fits into a weight-loss routine
| What it realistically does | What it doesn't do | |
|---|---|---|
| Calorie burn | ~140 cal/hour, passive | Replace a 300-600+ cal workout |
| Recovery | Eases post-workout muscle soreness, may support training consistency | Build muscle or raise resting metabolism |
| Scale weight | Temporary drop from sweat/water loss | Actual fat loss |
| Habit support | A relaxation reward that can help you stick to a routine | A workout substitute on rest days |
The most defensible role for a hot tub in a weight-loss plan is recovery, not calorie burn: a warm soak after a workout can ease soreness (see our hot tub after a workout guide for timing and temperature), which for some people makes it easier to stay consistent with training over weeks and months. That’s an indirect, habit-level benefit — not the direct “soak it off” mechanism the marketing implies.
Intex PureSpa Plus
- An affordable way to build a consistent post-workout soak habit without a $2,500+ plug-and-play spa.
- Built-in hard-water system and Fiber-Tech laminated PVC hold up to regular use.
- App control lets you have it pre-heated and ready right when a workout ends, which matters more for consistency than any single session's calorie count.
Building out a home gym routine to go with the tub? Try Prime free for 30 days for free two-day delivery on the resistance bands, foam roller, or scale you still need.
The bottom line
A hot tub burns real but modest calories — about 140 per hour per the Loughborough research, roughly a 30-minute walk’s worth — through your body’s own cooling response, not any fat-burning property of warm water. It’s not a workout substitute and any scale drop immediately after a soak is water, not fat. Where a hot tub genuinely helps a weight-loss effort is recovery and habit consistency: easing soreness after real exercise so you keep showing up for it. If muscle recovery specifically is your focus, see our hot tub after a workout guide for the ideal timing and temperature. If general relaxation and stress are more the goal, our hot tub for stress relief guide covers the nervous-system side of a warm soak. Still deciding whether a hot tub is worth the cost and upkeep at all? Our are inflatable hot tubs worth it guide breaks down the honest tradeoffs.