Methodology
The estimate, with its workings shown.
This calculator turns a resting-energy equation into a practical daily starting range. It is transparent about the maths—and about what the maths cannot know.
Step 1
Estimate resting energy
We use the Mifflin–St Jeor equation to estimate resting metabolic rate (RMR), also called resting energy expenditure: the energy the body is expected to use at rest. It is often labelled “BMR” by consumer calculators, but the source paper describes REE.
Male constant: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Female constant: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
The equation requires one of two sex-specific constants and cannot represent every body or lived experience. That is a limitation of the equation, not a judgement about identity. The original study included adults aged 19–78; a later American Journal of Clinical Nutrition validation paper summarises its reported BMI range as 17–42. The calculator refuses weight-and-height combinations outside that study range instead of presenting an unsupported ordinary result. Ages outside 19–78 remain an extrapolation and must be treated with extra caution pending independent dietitian review. Read the original Mifflin research paper on PubMed.
New to BMR, RMR, REE, TDEE or kcal? Use the acronyms and terms guide, then read calorie calculators explained for a fuller introduction.
Step 2
Approximate a whole day
Estimated RMR is multiplied by the activity factor selected in the calculator. The result is estimated total daily energy expenditure (TDEE).
| Choice | Factor | Plain-English guide |
|---|---|---|
| Mostly seated | 1.2 | Little purposeful activity in a typical week |
| Lightly active | 1.375 | Roughly 1–3 active days each week |
| Moderately active | 1.55 | Roughly 3–5 active days each week |
| Very active | 1.725 | Roughly 6–7 active days each week |
| Highly active | 1.9 | A physically demanding job as well as regular training |
These factors are broad conventions, not measurements. Work, caring, walking, training, illness, sleep and day-to-day movement can make the true value different. Choose the description that matches an average week, not your busiest day. Our activity-level guide gives practical examples and common traps.
Step 3
Apply a gentle goal
Maintenance leaves estimated TDEE unchanged. The “lose gently” and “gain gently” choices apply a 10% reduction or increase. The result also shows a range of 5% either side so an inherently uncertain estimate does not look falsely exact.
The macro figures are an optional balanced illustration, not required targets and not personalised medical advice. Food preference changes shopping suggestions only; it never changes the calorie equation. If the calculated target falls below 1,200 or above 5,000 kcal/day, the general tool refuses to present it and directs the visitor to individual support. Near those boundaries, the displayed uncertainty range is clipped so it never suggests a value outside the tool’s own presentation limits.
Because this unsupervised tool cannot assess medical history, nutritional adequacy or individual clinical risk, it withholds goal targets below 1,200 kcal/day. This is a conservative product safety boundary, not a universal medical threshold or a promise that every higher result is suitable.
For wider international context, see the World Health Organization's guidance on healthy diets and its overview of overweight and obesity. Local clinical guidance may differ.
Limits
What the estimate does not measure
- Body composition, metabolic adaptation or an individual’s measured energy expenditure.
- Pregnancy, breastfeeding, growth, frailty, illness, recovery, medication or clinical nutrition needs.
- Whether weight change is appropriate or safe for a particular person.
- Allergies, intolerances, nutrient deficiencies, cultural needs or eating-disorder risk.
Use the result as a starting hypothesis. Keep conditions reasonably consistent for 14 days, observe the trend and make only a small adjustment if appropriate. Sudden or unexplained weight change, faintness, persistent fatigue, distress around eating or any concerning symptoms call for professional support—not a tighter target.
Review status
Evidence without invented endorsement
Formula and safety sources were checked for this general-information release on 10 September 2026. That review supports the stated scope and limitations; it is not clinical endorsement or individual medical advice. See our editorial policy for the publication standard.