Maintenance Calorie Calculator

Think of your body like a building with a baseline electricity bill. Even when nothing is happening inside — no activity, no movement — the lights, HVAC, and servers still run. That baseline draw is your resting metabolic rate, or BMR. It accounts for roughly 60-70% of the calories you burn every day just by being alive.

On top of that baseline, every movement you make costs energy — walking to the kitchen, typing, a gym session, fidgeting. The total of your baseline plus all that movement is your total daily energy expenditure, or TDEE. That is what this calculator computes. The Mifflin-St Jeor formula estimates your BMR from your weight, height, age, and biological sex, then multiplies it by an activity factor that approximates how much extra energy your lifestyle demands.

The result is your maintenance calories — the intake level where your weight should stay flat. Eat above it consistently and you gain weight. Eat below it and you lose. The number itself is not magic; it is a starting estimate. Real metabolisms vary by 10-15% from the formula even in healthy adults, which is why the result carries an estimated label rather than exact.

Use this calculator when you are setting up a diet phase — whether you are cutting, bulking, or just trying to stop unintentional weight gain or loss. It gives you the reference point everything else is calculated from. Without knowing maintenance, any calorie target is a guess.

Also use it when life changes your activity level — a new job, an injury, a training block ending, a move to a more walkable city. Any of these can shift your TDEE by 200-400 calories per day, enough to change your body weight over months without you realizing why.

Do not use this as a clinical or medical nutrition tool. The formula was validated on healthy adults aged 15-80. It is not appropriate for people with thyroid conditions, metabolic disorders, eating disorder recovery, or anyone under active medical nutrition therapy. In those cases, work with a registered dietitian who can account for factors this formula cannot see.

The most common mistake is picking the wrong activity multiplier. Most people select sedentary or lightly active because they feel they do not exercise much, while forgetting that a job requiring standing, walking a dog, or chasing kids adds significant caloric output. Underestimating activity leads to a maintenance number that is too low — and then confusion when eating at that level still causes weight gain.

A second mistake is treating the result as exact and adjusting in large steps. Because no formula predicts an individual metabolic rate precisely, jumping from maintenance to a 1,000-calorie deficit immediately is an overcorrection. A 300-500 calorie adjustment gives you room to observe the actual response before making further changes.

The third mistake is running this calculation once and never revisiting it. As your weight changes, your BMR changes. A 20 lb loss can shift maintenance by 150-200 calories, which is enough to stall progress if you are still eating to your original number. Recalculate every time your weight changes by more than 10 lb.

The Mifflin-St Jeor formula calculates BMR as follows:

For males: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5 For females: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161

Once BMR is calculated, it is multiplied by an activity factor to produce TDEE: - Sedentary: BMR x 1.2 - Lightly active: BMR x 1.375 - Moderately active: BMR x 1.55 - Very active: BMR x 1.725 - Extremely active: BMR x 1.9

For the lean mass output, the calculator takes your body fat percentage, derives lean body mass in pounds, and divides TDEE by that number. This gives you calories per pound of lean mass — a metric used by coaches to scale intake when body composition changes over time without recalculating from scratch.

The activity multipliers were derived from doubly labeled water studies on population averages — they describe what people typically burn at each stated activity level, not what you burn. High responders and low responders to exercise both exist. Additionally, the Mifflin-St Jeor formula implicitly assumes a body composition that matches population norms for a given weight. At very high or very low body fat percentages, the formula diverges from measured RMR because lean mass is the actual metabolic engine — which is why the lean mass calories output becomes more useful than the raw TDEE for athletes tracking recomp phases.