Estimated Energy Requirement is the Institute of Medicine's standardized formula for how many calories a person needs each day to maintain their current weight, based on age, sex, weight, height, and physical activity level. Published in the 2005 Dietary Reference Intakes for Energy report, EER equations were derived from doubly labeled water studies — a gold-standard method for measuring real-world total energy expenditure — across children, adolescents, and adults, with separate adjustments for pregnancy and lactation.
How EER is calculated
EER equations combine a fixed constant, an age-adjustment term, and a physical-activity (PA) coefficient multiplied by weight and height terms. Adults use one equation set (with the PA coefficient ranging from 1.00 at Sedentary up to 1.45-1.48 at Very active); children and adolescents use a separate equation set with different coefficients and a small fixed "growth constant" (+20 or +25 kcal/day) that accounts for the extra energy needed for normal growth.
Because the equations were fit to age-band-specific and sex-specific data, mixing tables (for example, applying the adult PA coefficients to a 10-year-old) would give a systematically wrong answer — this calculator automatically routes each input set through the correct equation and PA table for its age band.
EER vs. TDEE and BMR-based calculators
Many popular calorie calculators compute Basal Metabolic Rate (BMR) first — using formulas like Mifflin-St Jeor or Harris-Benedict — and then multiply by an activity factor to get Total Daily Energy Expenditure (TDEE). EER is conceptually similar but is the IOM's own directly-fit formula, built from measured total energy expenditure rather than from a separate BMR estimate scaled up. In practice, EER and a well-chosen TDEE calculation often land close together for a given adult, but EER is the specific reference equation cited in U.S. dietary guidance and clinical nutrition literature.
Pregnancy and lactation adjustments
During pregnancy, the IOM adds no adjustment in the first trimester (when energy needs change very little), +340 kcal/day in the second trimester, and +452 kcal/day in the third trimester, reflecting accelerating fetal and maternal tissue growth. During lactation, it adds +330 kcal/day for the first six months postpartum (assuming some energy comes from fat stored during pregnancy) and +400 kcal/day from 7-12 months, when that stored-fat offset is assumed to be smaller. These adjustments apply only to the adult female equation — the IOM does not publish separate pregnancy/lactation adjustments for adolescents in this framework.
Limits and how to use the number
EER is a population-level estimate for a healthy person of a given age, sex, weight, height, and activity level — it is not personalised to your metabolism, body composition, medical conditions, or medications, all of which can shift real energy needs. It is for general education and informational purposes only, not medical, nutritional, or clinical advice, and it does not replace guidance from a registered dietitian or physician, particularly during pregnancy, lactation, or when managing a medical condition.
Use your EER as a starting reference point, not a fixed prescription: track your actual weight trend over several weeks against your intake, and adjust from there.