Calorie Deficit and Working Out: How to Combine Them

With a calorie deficit and working out together, take most of the gap from food, because a workout adds less than it feels like. Say an 80 kg (176 lb) adult walks briskly for 150 minutes a week. That uses about 760 kcal beyond rest, or 109 kcal a day. The AHA/ACC/TOS guideline puts the usual deficit at 500 kcal a day, so the walk covers about a fifth of it. Exercise still has a place in the plan, just for other jobs.

How many calories does a workout really use?

A half hour of brisk walking adds about 152 kcal for an 80 kg adult, and a half hour of running adds about 300. The Compendium of Physical Activities gives every activity a MET value, where one MET is 1 kcal per kilogram of body weight per hour. Multiply the MET by your weight in kilograms and by the hours you moved. That total includes the energy you’d spend sitting still anyway, so I subtract one MET to get what the workout itself adds.

Activity, 30 minutes at 80 kg	MET	Total kcal	Extra kcal beyond rest
Walking, 3.5 to 3.9 mph, brisk	4.8	192	152
Running, 5.0 to 5.2 mph	8.5	340	300
Weight training, multiple exercises, 8-15 reps	3.5	140	100

Now the week. A brisk walk for 150 minutes is 2.5 hours, so 3.8 × 80 kg × 2.5 h = 760 kcal beyond rest, about 109 kcal a day. At 60 kg the same walk adds 570 kcal, and at 100 kg it adds 950.

Pick the activity you really do, find its MET in the Compendium and do the sum once, so you know what a sensible number looks like before a screen shows you one.

How do a calorie deficit and working out fit together?

Treat exercise as a small share of the gap. The guideline says lifestyle programs typically aim for a deficit of at least 500 kcal a day, plus 150 minutes a week of aerobic activity. For keeping lost weight off beyond a year, it suggests 200 to 300 minutes. Over a week a 500 kcal gap comes to 3,500 kcal, and the walking dose above pays for about 22% of it. What a calorie deficit is explains where that 500 comes from.

The same 3,500 kcal week can be built four ways for the 80 kg adult. The exercise figures are estimates from the formula, not measurements.

Plan	Exercise, extra kcal a week	Food cut a week	Food cut a day
Food only	0	3,500	500
Food plus 150 minutes of brisk walking	760	2,740	391
Walking plus two 30-minute weight sessions	960	2,540	363
Three 30-minute runs plus two weight sessions	1,100	2,400	343

With exercise in the plan, the daily food cut shrinks by 109 to 157 kcal, about what a small snack holds.

A meta-analysis by Murphy and Koehler concluded that people lifting to keep lean mass during weight loss should avoid deficits above 500 kcal a day, so I count the workouts toward that 500 and never add them on top. A 500 kcal food cut plus 1,100 kcal of weekly exercise makes 657 kcal a day, which is past that line. Keep the pace inside the NHS range of 0.5 to 1 kg (1 to 2 lb) a week as well. What that range looks like in calories is in NHS calorie deficit advice.

The floor applies as well. The guideline’s usual targets start at 1,200 kcal for women and 1,500 for men, and I treat those as the lowest a day should go. If a hard session leaves you under, add food. Write the plan as one number, food plus workouts, and keep it at 500 kcal a day or less.

To set the food side of that number, enter your age, height, weight and activity in the calorie calculator. It applies the NASEM 2023 equations and floors its targets at 1,200 calories for women and 1,500 for men.

Should I add my workout calories to my food budget?

Not workout by workout. Set the food target from your usual week and judge it by the two-week weight trend. The workout number is the shakiest figure in the plan.

A 2017 study of seven wrist devices checked them against lab measurements of energy use in 60 volunteers. Median errors across activities ranged from 27.4% to 92.6%, depending on the device. None got under 20%. Even the best of them, with that 27.4% median miss, could be off by roughly 110 kcal on a 400 kcal workout. If the watch overshoots and you eat all 400 back, the extra is yours to carry.

I keep the food plan fixed and let the weekly averages show whether the gap is real. If you feel worn out for weeks, that’s a reason to eat more and talk to your doctor, not to add sessions.

Why am I not losing weight with a calorie deficit and exercise?

Often the real gap is smaller than the planned one. Two numbers explain most of that, and both are easy to get wrong by hand.

The first is intake. A 1992 study in the New England Journal of Medicine measured ten adults for two weeks. All of them said they couldn’t lose weight on under 1,200 kcal a day. Their energy use was normal, within 5% of prediction. They had under-reported food by 47% on average and over-reported exercise by 51%. The authors found no metabolic problem. The gap was in the notes, which is no character flaw, because nobody remembers a day to the gram.

Training itself brings the second. A 2012 energy balance analysis found that most exercise trials produced small losses. The authors blamed low exercise doses, made worse by a rise in calorie intake.

Test your own week. Weigh the food you eat for seven days and weigh yourself on three or more mornings. Then compare the average weight of two weeks in a row. Whether you can gain weight in a calorie deficit overnight is a fair worry, and the averages answer it. If the average hasn’t moved, change the food by 100 to 200 kcal a day before you add another session. Why you’re not losing weight in a calorie deficit covers the other usual causes.

How much protein and lifting do I need in a deficit?

Aim for 1.2 to 1.6 g of protein per kg of body weight, and lift on two days a week. The Dietary Guidelines for Americans set the protein range, which is 96 to 128 g a day at 80 kg. The CDC asks adults for at least two days of muscle-strengthening activity.

People who train can go higher. The International Society of Sports Nutrition calls 1.4 to 2.0 g/kg sufficient for most exercising people, which is 112 to 160 g at 80 kg.

In the Murphy and Koehler review, lean mass gains were smaller in a deficit than without one, while strength gains were similar. In a deficit, then, lifting mostly holds on to the muscle you already carry.

When does exercise stop helping?

It stops helping when it turns into payment for food. A missed workout that makes you cut dinner is a warning sign, and so is a big meal that sends you out for a run. A calculator can’t fix that link.

A few readers shouldn’t use these numbers at all. If you have a heart condition, are pregnant or are recovering from an injury, your doctor sets the activity and calorie plan. People under 18 fall outside these numbers too, which are meant for adults.

For everyone else the next step is small. Do the MET sum for your usual activity, plan a food cut that fits inside 500 kcal a day with it, and check the result against two weekly averages. I leave the watch’s own calorie figure out of that sum and use the MET estimate instead.

If counting calories has started to feel hard to stop, or eating feels out of control, talk to someone: ANAD in the US (1-888-375-7767), Beat in England (0808 801 0677), NEDIC in Canada (1-866-633-4220) or the Butterfly Foundation in Australia (1800 33 4673). If you’re in danger right now, call your local emergency number. Other UK numbers and crisis lines are on our crisis support page.