How Many Calories Do I Burn in a Day?

Most of it is just staying alive

A 35-year-old man, 5 ft 8 in, 160 lb, lightly active burns about 2,248 calories a day.

1,635 of those happen lying still. Heart, breathing, temperature, brain. That's 73% of the total, before he gets out of bed — which is the part that surprises people who assumed exercise was the main event.

The arithmetic

The Mifflin-St Jeor equation, published in 1990 and fitted to 498 healthy adults aged 19–78:

BMR = 10 × kg + 6.25 × cm − 5 × age, then +5 for men or −161 for women.

That constant is the only difference between the two versions.

160 lb = 72.57 kg · 68 in = 172.72 cm

(10 × 72.57) + (6.25 × 172.72) − (5 × 35) + 5 = 1,635

TDEE = BMR × activity factor. At lightly active (1.375): 1,635 × 1.375 = 2,248

The input you'll get wrong

The activity multiplier, and it isn't close.

Factor	Level
1.2	Sedentary — desk job, little exercise
1.375	Lightly active — light exercise 1–3 days
1.55	Moderately active — moderate exercise 3–5 days
1.725	Very active — hard exercise 6–7 days
1.9	Extremely active — hard daily exercise or physical job

Stepping from lightly to moderately active changes the answer by about 13% — 287 calories on the numbers above. That single dropdown moves the result far more than the choice of BMR equation does, and it's the one you're guessing at.

Self-reported activity is also consistently overstated. A desk job with three gym sessions a week is "lightly active" more often than anyone wants it to be; "very active" means hard training most days or manual work.

If you're hesitating between two, pick the lower one.

What the equation can't see

It takes height, weight, age and sex. That's the whole input, which means it cannot know your body composition.

Muscle burns more at rest than fat does. So at the same height and weight, a very muscular person has their BMR underestimated, and someone carrying more body fat has theirs overestimated.

It's the same blind spot BMI has, for exactly the same reason — those four numbers can't tell muscle and fat apart. Equations that use lean mass exist, but they need a body-fat measurement first, which is a harder thing to get accurately than most people expect.

Your own data beats the equation

This is the most useful thing on the page.

Mifflin-St Jeor was fitted to 498 people in 1990. You are not in that dataset. Real metabolic rates vary meaningfully around any prediction.

So: if your weight has been stable for several weeks, what you're currently eating IS your maintenance. That's a direct measurement. The equation is a prediction from a thirty-five-year-old average.

If they disagree by a few hundred calories, that's completely normal — and the equation is the one that should give way.

Track for at least two weeks. One week is mostly water.

Why this doesn't tell you what to eat

You'll notice the calculator reports what you burn and stops there.

Turning a burn figure into an intake target involves your goals, your timeline, how sustainable a given rate is for you, and any medical conditions in play. That's a genuinely different question, and it belongs with a doctor or a registered dietitian who can see the whole picture — not with a multiplication on a web page.

What this figure is good for is orientation: knowing roughly where maintenance sits, and knowing that most of it happens whether you go to the gym or not.

Print the energy balance log and give it a fortnight. The number you measure will beat the number you calculated.

Not medical advice. This estimates energy expenditure from a population equation; it makes no assessment of your health and doesn't account for medical conditions, medication, pregnancy or disordered eating.

Sources: NutriAdmin — the Mifflin-St Jeor equation · Inch Calculator — Mifflin-St Jeor