Calorie deficit calculator

To lose fat you need to eat a bit less than you burn. This calculator estimates how many calories you burn a day (your TDEE), then shows a mild and a moderate deficit — and flags when a target drops too low.

How the calculator works

First it estimates your basal metabolic rate (BMR) — the energy your body uses at rest — with the Mifflin-St Jeor equation. A 2005 systematic review found it the most accurate of the common equations, predicting resting metabolism within 10% for most healthy adults.

Then it multiplies BMR by an activity factor (1.2 for sedentary up to 1.9 for very physical lives) to get your total daily energy expenditure, or TDEE. Eating around your TDEE keeps your weight roughly stable.

How big should a calorie deficit be?

A deficit of 250–500 kcal a day is a common, sustainable starting point. As a rough rule, 500 kcal a day adds up to about half a kilo (one pound) a week at first. Progress slows over time as your body gets lighter and adapts, so the weekly figure is a starting estimate, not a promise.

Bigger deficits cost more muscle and are harder to stick to. That's why the calculator flags any target below your resting metabolism or below common minimums (about 1,200 kcal for women and 1,500 kcal for men) — below those, talk to a professional.

Keep the muscle while you lose the fat

The scale can't tell fat loss from muscle loss. Eating enough protein and keeping up strength training while in a deficit helps make sure most of the weight lost is fat. Track your waist and body fat as well as your weight: if the waist is shrinking, the deficit is working.

See if the deficit is taking fat or muscle

Trainr builds meals around your calorie and protein targets, logs food from a photo, and tracks body fat and measurements from two photos — so you know the weight you lose is fat. The first scan is free.

Start tracking — free

Common questions

How do I calculate my calorie deficit?

Estimate your maintenance calories (TDEE) from your BMR and activity level, then subtract 250–500 kcal a day. This calculator does both steps for you.

What is TDEE?

Total daily energy expenditure: everything you burn in a day — resting metabolism, digestion, daily movement and exercise.

Is a 1,000-calorie deficit safe?

For most people it's too aggressive to sustain and costs muscle. Unless you're supervised by a professional, a 250–500 kcal deficit is the safer default.

Why am I not losing weight in a deficit?

Equations can be off by 10% or more, water retention can hide fat loss for a week or two, and logging is often less precise than it feels. Give it 2–3 weeks, watch your waist too, then adjust by 100–200 kcal.

Start with a modest deficit, keep protein high, and judge progress by your waist and body fat — not the scale alone.

Sources

Mifflin MD, St Jeor ST, Hill LA, et al. (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/2305711/
Frankenfield D, Roth-Yousey L, Compher C (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. https://pubmed.ncbi.nlm.nih.gov/15883556/

More free tools

Body fat calculatorEstimate your body fat percentage with a tape measure — Navy or one-site Army method.Body fat percentage picturesSee what different body fat levels look like for men and women, side by side.Protein calculatorHow much protein you need per day and per meal, for your goal and activity.FFMI calculatorFat-free mass index and lean body mass — a better muscle measure than BMI.Waist-to-height ratio calculatorIs your waist less than half your height? The simple check guidelines now use.

Trainr is a wellness tool, not a medical device. These calculators give estimates for self-tracking, not a diagnosis. For medical questions, talk to a professional.