The calculator estimates energy needed to maintain your current weight. It combines a resting-energy equation with a whole-day activity assumption. Both parts introduce uncertainty; the result is a starting estimate rather than a measurement.
Resting energy comes first
We use the simplified Mifflin–St Jeor equations published in 1990. With current weight W in kilograms, height H in centimetres and age A in years:
Male: REE = 10 × W + 6.25 × H − 5 × A + 5
Female: REE = 10 × W + 6.25 × H − 5 × A − 161
REE means resting energy expenditure, expressed here in kcal/day. It estimates energy used at rest. It is not a measured basal metabolic rate (BMR), whose measurement conditions are stricter, and it is not a recommended minimum intake. Total daily energy expenditure (TEE, also called TDEE) includes resting energy, food processing and activity.
The original equation was derived from 498 healthy adults. Its Male and Female categories are historical regression categories, not a gender profile. The tool does not infer which category applies or provide a rule for hormone treatment. A population equation cannot promise an individual's accuracy.
Mifflin et al. (1990) gives the equations and study population. Dietary Reference Intakes for Energy (2023), chapter 4 explains resting, basal and total energy.
Activity is an explicit assumption
Estimated maintenance (TEE) = estimated REE × chosen factor
The factor covers the whole day: work, walking, household tasks and exercise. Because it represents total energy relative to rest, we do not add separate exercise calories or another percentage for food processing.
- 1.4 — Lower daily movement
- A lower comparison assumption.
- 1.6 — Mostly sitting plus some moderate activity
- The NIH planner describes its 1.6 reference as mostly seated school or work with moderate activity, such as walking or cycling, at least weekly.
- 1.8 — Higher daily movement
- A higher comparison assumption.
These three scenarios show how the assumption changes the calculation. They are not a personal confidence interval, an automatic classification or a complete list of activity patterns. Actual needs can fall outside them. The 2023 DRI applications chapter describes the difficulty of reliably classifying an individual's physical activity level.
Check the denominator when comparing factors. The Hall et al. (2011) methods appendix, page 4 (PDF) defines PAL as total energy expenditure divided by resting metabolic rate. Other PAL definitions, including the DRI chapter 4 definition, use BMR as the denominator. They are not automatically interchangeable.
This tool uses a static REE × factor calculation. It does not implement the full NIH Body Weight Planner, which models body-weight and metabolic changes over time. The NIH reference description informs our 1.6 label; its full model's validation does not validate this smaller tool or your chosen factor.
Units and rounding
US input is converted before calculating: kilograms = pounds × 0.45359237; centimetres = (12 × feet + inches) × 2.54. These use the exact international pound and inch conversions documented by NIST, Guide to the SI, appendix B.8. The calculation retains full numeric precision internally.
Maintenance results are rounded to the nearest 50 kcal/day, with halfway values rounded up: 2,725 becomes about 2,750. This makes the estimate easier to read; it is not a ±25 kcal accuracy claim. Unrounded model values appear in the calculator's method details.
For example, 80 kg, 180 cm, age 40 and the Male equation give REE of 1,730 kcal/day. At factor 1.6, the model value is 2,768, displayed as about 2,750 kcal/day. This is an arithmetic example, not a personal intake recommendation.
Where this small tool stops
We accept ages 19–78 as a product limit. It is not a medical boundary or a claim that estimates are valid for every person within it. Height (100–250 cm) and weight (30–300 kg) limits catch input errors; they do not define healthy size or proven accuracy.
The calculator is not intended for pregnancy or breastfeeding, clinical nutrition treatment, unusual or extreme body composition, or exceptional athletic workloads. It does not diagnose, prescribe intake, plan weight change or replace individual clinical assessment. The 2023 DRI special-considerations chapter explains why some circumstances require different information or methods.
Primary sources checked: . This is a source check, not a medical review or endorsement by the cited organisations.