Harris-Benedict Calculator — BMR and Calories

Harris-Benedict is the original basal metabolic rate equation, published in 1919 and still built into a surprising amount of clinical software. The calculator below runs the 1919 coefficients exactly as printed — which matters, because a second set circulates under the same name. Enter your details:

The equation as published

Weight in kilograms, height in centimeters, age in years, result in kcal/day:

• Men: BMR = 66.47 + 13.75 × weight + 5.003 × height − 6.755 × age
• Women: BMR = 655.1 + 9.563 × weight + 1.850 × height − 4.676 × age

Note how different the two lines are — this is not one formula with a sex constant bolted on the end, the way Mifflin-St Jeor is. Every coefficient changes, and the women’s height term (1.850) is a third of the men’s (5.003). That asymmetry is an artifact of fitting two separate regressions to two small samples, not a physiological claim.

Worked out, in pounds and feet

A 35-year-old man at 180 lb and 5 ft 10 in. Convert first: 180 lb ÷ 2.205 = 81.6 kg, 70 in × 2.54 = 177.8 cm.

66.47 + 13.75 × 81.6 + 5.003 × 177.8 − 6.755 × 35 = 66 + 1,122 + 890 − 236 = 1,842 kcal/day.

A 35-year-old woman at 150 lb and 5 ft 5 in (68.0 kg, 165.1 cm):

655.1 + 9.563 × 68 + 1.850 × 165 − 4.676 × 35 = 655 + 650 + 305 − 164 = 1,447 kcal/day.

Two equations wearing the same name

In 1984, Roza and Shizgal refitted Harris and Benedict’s original data and published a different set of coefficients. Both are labeled “Harris-Benedict” on the web, so the same person can get two answers depending on which calculator they opened:

	1919, as published	Roza & Shizgal 1984 revision
Men, constant	66.47	88.362
Men, weight	13.75	13.397
Men, height	5.003	4.799
Men, age	− 6.755	− 5.677
Women, constant	655.1	447.593
Women, weight	9.563	9.247
Women, height	1.850	3.098
Women, age	− 4.676	− 4.330

For the man above, the revision returns 1,836 kcal/day against the original’s 1,842 — close. For the woman, 1,436 against 1,447. Small gaps in these examples, but they are not always small, and if you are comparing your number against something you calculated last year, you should know which set produced it. This page uses the 1919 version throughout.

Adding the activity factor

Neither version gives you calories to eat. Both give a resting floor, which then gets multiplied:

Activity level	Factor	Man in the example (1,842 BMR)
Sedentary	× 1.2	2,210 kcal/day
Light, 1 to 3 days/week	× 1.375	2,533 kcal/day
Moderate, 3 to 5 days/week	× 1.55	2,855 kcal/day
Intense, 6 to 7 days/week	× 1.725	3,177 kcal/day
Very intense	× 1.9	3,500 kcal/day

Where it stands against Mifflin-St Jeor

Mifflin and colleagues built their 1990 equation on 498 adults aged 19 to 78, half of them with obesity, all measured by indirect calorimetry — and reported plainly that the 1919 Harris-Benedict equations overestimated measured resting energy expenditure by 5 percent. Our worked examples show exactly that drift: 1,842 against Mifflin’s 1,757 for the same man (a gap of 85 kcal, 4.8%), and 1,447 against 1,375 for the same woman (72 kcal, 5.2%).

Five percent a day is not nothing. Held for a year, an 85 kcal daily overestimate is the difference between a plan that works and one that quietly does not. The 2005 systematic review that compared the field found Mifflin-St Jeor the most reliable of the lot, with the narrowest error range — which is why the Mifflin-St Jeor calculator is the one to start a new estimate with, and why the main BMR calculator defaults to it.

Harris-Benedict earns its place for one honest reason: consistency. If your training log, your clinic’s software or your spreadsheet has used it for years, switching mid-stream makes your own history unreadable. Comparing yourself to yourself beats being 5% closer to a lab value you were never going to measure anyway.

This content is informational and does not replace evaluation by a physician or registered dietitian.