Understand your numbers.
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BMR, TDEE, and calorie deficit calculators, together. Enter your details once to explore how resting energy, everyday activity, and a change in intake connect.
For adults aged 18 and over. These estimates are not designed for pregnancy, breastfeeding, or an active or suspected eating disorder. Medical conditions and medicines can also change your needs.
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What these estimates can tell you.
Use the numbers to understand the relationship between rest, activity, and intake. A calculator cannot establish whether weight loss or a particular intake is right for you.
How is BMR calculated?
We use the Mifflin–St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age in years, then add 5 for the male equation or subtract 161 for the female equation.
Although commonly called a BMR calculator, this formula estimates resting energy expenditure. Strict basal metabolic rate is measured under more controlled conditions. Values are rounded to the nearest calorie only for display.
How do activity and TDEE work?
TDEE is the resting estimate multiplied by the activity factor you select. These broad activity categories are approximations, not measured energy expenditure.
- Mostly sitting (×1.2): Little or no exercise; mostly seated work.
- Lightly active (×1.375): Light exercise 1–3 days a week, such as easy walks or gentle cycling.
- Moderately active (×1.55): Moderate exercise 3–5 days a week, such as brisk walks, swimming, or gym sessions.
- Very active (×1.725): Hard exercise 6–7 days a week or a physically demanding job.
- Exceptionally active (×1.9): Very hard daily exercise plus physical work, or training twice a day.
Choosing a higher factor changes the estimate; it does not establish that you need that intake.
What do the calorie deficit simulations mean?
Each row multiplies your current weight by a different weekly percentage to give a weight-loss scenario. We multiply that amount in kg by approximately 7,700 kcal and divide by seven to estimate a daily deficit, then subtract it from TDEE. For example, 0.5% of 80 kg is 0.4 kg per week, corresponding to about 440 kcal per day. Maintenance uses no reduction.
This static conversion does not predict actual weekly loss. Changes in water, body composition, and energy expenditure affect the result; see Hall’s research on energy deficits and weight loss. The pace labels describe the scenarios in this tool, not clinically validated categories.
The tool flags reductions above 25% of TDEE. Positive deficit intakes below 1,200 kcal for the female equation or 1,500 for the male equation are shown with a pastel highlight and a low-intake warning. Deficit intakes are still withheld when BMI is below 18.5 or the calculation produces zero or negative intake. These are tool guardrails, not universal safety thresholds. The AHA/ACC/TOS adult weight-management guideline discusses calorie ranges within individualized care.
How should I use the estimates?
Treat the result as a rough reference. Everyday movement, body composition, health, and changes in weight can affect your needs. If you need a personal eating target, discuss your circumstances with a registered dietitian or other qualified health professional.
The NIDDK Body Weight Planner offers a more detailed model of changing energy needs over time, for adults who are not pregnant or breastfeeding.