How to use the Calorie Deficit Calculator
- 1 Choose units and enter your age, height, weight and the sex coefficient used by the Mifflin–St Jeor equation.
- 2 Select a typical activity level and a goal adjustment relative to estimated maintenance calories.
- 3 Optionally choose a BMR formula and macro split to view daily calorie and macronutrient estimates.
Estimate calories for a weight goal
This calculator estimates basal metabolic rate (BMR), daily maintenance calories and a calorie target for a selected goal. It also converts a selected carbohydrate, protein and fat split into estimated grams per day. Results depend on your inputs and on broad formula assumptions.
How the estimate is calculated
By default, the tool estimates BMR with the Mifflin–St Jeor equation, which uses weight, height, age and a male or female equation coefficient. It multiplies this result by an activity factor to estimate maintenance calories. This equation was developed to predict resting energy expenditure in healthy adults (original study on PubMed).
In Advanced settings, you can select Katch–McArdle. This estimates resting energy from lean body mass, calculated from your weight and the body-fat percentage you enter: BMR = 370 + 21.6 × lean body mass in kg. The equation therefore depends on the quality of that body-fat estimate (research paper discussing the equation).
The activity multiplier is then applied to BMR for an approximate maintenance value. The selected goal adjusts maintenance by 10% or 20% in either direction, or leaves it unchanged. These are adjustable calculator scenarios, not a personalized recommendation or prediction of weight change.
Macronutrient estimates
The macro presets divide the estimated calorie target into percentages for carbohydrates, protein and fat. The calculator converts those calories to approximate grams using 4 kcal per gram for carbohydrates and protein and 9 kcal per gram for fat. These presets are examples for comparing the math, not personalized nutrition targets.
Understand calorie deficit results
A calorie deficit means taking in less energy than your body uses over time (NHS overview of calories and weight loss). The weekly difference shown here is only the daily arithmetic difference multiplied by seven; it does not predict a specific amount of weight loss. Estimated maintenance, food labels, portion sizes and daily activity all have uncertainty.
General information for adults
This tool is intended for adults and provides estimates, not medical advice or a prescribed diet. Energy needs and appropriate goals differ with health, age, activity and other factors. Seek individualized guidance from a qualified healthcare professional, particularly if you have a medical condition, are pregnant, or are managing a history of disordered eating. Do not use calorie-restriction settings for children or teenagers.
Frequently asked questions
How does this calorie deficit calculator work?
It estimates BMR, applies an activity factor to estimate maintenance calories, then adjusts maintenance by the selected 10% or 20% goal scenario.
Which BMR formula should I choose?
Mifflin–St Jeor uses age, height, weight and a sex coefficient. Katch–McArdle uses estimated lean body mass, so its result depends on the accuracy of your body-fat input. Both are predictions, not measurements.
How are the macro grams calculated?
The selected percentages allocate the calorie target to carbohydrates, protein and fat. The calculator converts calories to grams using 4 kcal/g for carbohydrates and protein and 9 kcal/g for fat.
Does this result predict weekly weight loss?
No. The seven-day difference is just the daily calorie difference multiplied by seven. It is not a forecast of body-weight change.
Is the calorie target a recommendation?
No. It is a formula-based scenario for general information. It does not determine whether that intake or goal is appropriate for you.
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