How age and weight change a resting-energy estimate
Changing one input at a time reveals what the equation assumes. It does not tell you exactly how an individual body will change over time.
BMR calculator →Isolate the age term
Keep male equation parameters, 70 kg and 175 cm fixed. At age 30, the result is 1648.75 kcal per day; at age 40, it is 1598.75. The 50 kcal difference comes from the term −5 × age. This comparison holds every other input constant. It is not a promise that a particular person will experience precisely that metabolic change over the next decade.
Isolate the weight term
With the other inputs unchanged, raising weight from 70 kg to 75 kg increases the estimate by 50 kcal per day. The formula uses 10 kcal per kilogram in that term. It does not know whether the additional mass is muscle, fat or fluid, so the modeled difference should not be confused with a measured physiological response. Its simplicity is useful for explanation and also a source of uncertainty.
Enter observations separately from scenarios
Use current measured weight and completed age for a present-day estimate. If you substitute a hypothetical future weight, label the result as a scenario rather than an eating prescription. The age calculator can check completed years, while the calorie calculator shows how an activity assumption affects the total. Avoid treating any one equation input as a health goal merely because it produces a preferred result.
Try the calculators
- BMR calculator
Estimate resting energy with Mifflin–St Jeor.
- Age calculator
Find completed years and days between dates.
- Calorie calculator
Estimate maintenance energy for your activity level.