Schofield Equation Activity Factor Guide

The Schofield equation estimates your Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — and you multiply that number by an activity factor to estimate your total daily energy expenditure (TDEE). This calculator applies the standard Schofield weight-based formula, then lets you choose an activity multiplier from sedentary to very active, giving you a practical daily calorie target for weight maintenance.

Formula

The Schofield equation (1985) predicts BMR from body weight, age, and sex. For men aged 18–30, the formula is:

BMR = 15.057 × weight (kg) + 692.2

For women aged 18–30, it is:

BMR = 14.818 × weight (kg) + 486.6

These are the two most common variants for young adults. The equation changes with age brackets (e.g., 30–60 years uses different coefficients), but the calculator above uses the 18–30 coefficients for both sexes. The activity factor is a multiplier applied to BMR to estimate total daily energy expenditure (TDEE):

TDEE = BMR × Activity Factor

Where the activity factor is:

• Sedentary (little or no exercise): 1.2
• Lightly active (light exercise 1–3 days/week): 1.375
• Moderately active (moderate exercise 3–5 days/week): 1.55
• Very active (hard exercise 6–7 days/week): 1.725
• Extra active (very hard exercise, physical job, or training twice a day): 1.9

Worked Example

Using the calculator’s defaults: a 30-year-old man, 70 kg, moderately active (activity factor 1.55).

1. BMR = 15.057 × 70 + 692.2 = 1053.99 + 692.2 = 1746.19 kcal/day
2. TDEE = 1746.19 × 1.55 = 2706.59 kcal/day

Rounded to the nearest whole number, the calculator shows 2707 kcal/day. That is the estimated number of calories needed to maintain current weight at that activity level.

How the Activity Factor Works

The activity factor is a simple multiplier that accounts for the energy you burn through movement and exercise beyond your resting metabolism. It is not a precise measurement — it is a categorical scale. The categories are broad, and the difference between “lightly active” and “moderately active” can be subjective. For example, someone who walks 30 minutes a day might fit “lightly active,” while someone who does intense gym sessions five times a week would be “moderately active” or “very active.”

The factor assumes that your activity level is consistent throughout the week. If you exercise intensely on three days but are sedentary the rest of the week, the “lightly active” multiplier (1.375) is likely more accurate than “moderately active” (1.55).

How to Choose the Right Activity Factor

Choosing the correct factor is the most common source of error. Here are practical guidelines:

• Sedentary (1.2): Desk job, no exercise, minimal walking. Most of the day sitting or lying.
• Lightly active (1.375): Desk job, but you walk or do light exercise 1–3 times per week. This includes casual walking, yoga, or light cycling.
• Moderately active (1.55): You exercise moderately 3–5 times per week, or have a job that requires some walking (e.g., retail, teaching).
• Very active (1.725): Hard exercise 6–7 times per week, or a physically demanding job (e.g., construction, nursing).
• Extra active (1.9): Intense training twice a day, or a job that involves heavy manual labor (e.g., professional athlete, roofer).

When in doubt, choose the lower factor. Most people overestimate their activity level, leading to an overestimated calorie target.

Common Mistakes and Misconceptions

Mistake 1: Using the wrong age bracket. The Schofield equation has separate coefficients for ages 18–30, 30–60, and 60+. The calculator above uses the 18–30 coefficients. If you are 40, the correct BMR formula would be different (e.g., for men 30–60: BMR = 11.472 × weight + 873.1). This can change the result by 50–100 kcal/day.

Mistake 2: Confusing BMR with TDEE. BMR is the calories you burn at rest. TDEE includes activity. The activity factor is applied only after you have your BMR.

Mistake 3: Using pounds instead of kilograms. The formula requires weight in kilograms. To convert pounds to kilograms, divide by 2.2046. For example, 154 lbs ÷ 2.2046 = 69.85 kg.

Mistake 4: Rounding too early. If you round BMR to 1746 and then multiply by 1.55, you get 2706.3, which is close but slightly different from the calculator’s 2707. Keep full precision until the final step.

Limitations of the Schofield Equation

The Schofield equation was developed in 1985 using data from mostly European and North American populations. It tends to overestimate BMR in some ethnic groups and in people with higher body fat percentages. It also does not account for muscle mass — a muscular person will have a higher BMR than the formula predicts, while an obese person may have a lower BMR than predicted.

The activity factor is a rough estimate. It does not capture the intensity or duration of exercise precisely. Two people who both exercise 4 days a week could have very different calorie burns if one does 30 minutes of walking and the other does 60 minutes of high-intensity interval training.

For weight loss or gain, the Schofield equation provides a starting point, not a precise prescription. Individual metabolic rates vary by up to ±10% even among people of the same age, sex, and weight.

Alternatives to the Schofield Equation

Several other BMR equations exist, each with its own strengths:

• Mifflin-St Jeor: Developed in 1990, this equation is often considered more accurate for modern populations. For men: BMR = 10 × weight (kg) + 6.25 × height (cm) – 5 × age + 5. For women: BMR = 10 × weight (kg) + 6.25 × height (cm) – 5 × age – 161. It requires height, which the Schofield does not.
• Harris-Benedict: An older equation (1919, revised 1984) that also uses height, weight, and age. It tends to overestimate BMR in obese individuals.
• Katch-McArdle: Uses lean body mass instead of total weight, making it more accurate for athletes but requires body fat percentage.

The Schofield equation is still widely used because it is simple (only needs weight, age, sex) and works reasonably well for average adults. The Mifflin-St Jeor is a common alternative if you know your height.

Frequently Asked Questions

What is the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest, just to keep you alive — breathing, heartbeat, brain function. TDEE (Total Daily Energy Expenditure) is BMR plus the calories burned through physical activity, digestion, and daily movement. The activity factor bridges the two: TDEE = BMR × activity factor.

How do I convert my weight from pounds to kilograms?

Divide your weight in pounds by 2.2046. For example, 150 lbs ÷ 2.2046 = 68.04 kg. The calculator expects kilograms, so if you enter pounds, the result will be wildly wrong.

Is the Schofield equation accurate for athletes?

Not particularly. Athletes have a higher proportion of muscle mass, which raises BMR beyond what the formula predicts. The equation also does not account for the extra energy burned during intense training. For athletes, the Katch-McArdle formula (which uses lean body mass) or a direct measurement (indirect calorimetry) is more accurate.

Can I use this calculator for weight loss?

Yes, but with caution. The TDEE you get is an estimate of your maintenance calories. To lose weight, you typically eat 300–500 calories less than that per day, but this is not medical advice. Consult a healthcare professional before starting any diet. Also, the result is an estimate; adjust based on your actual weight changes over a few weeks.

Why does the calculator use only age 18–30 coefficients?

For simplicity, this calculator uses the 18–30 coefficients for all ages. If you are older, the Schofield equation has different coefficients (e.g., for men 30–60: BMR = 11.472 × weight + 873.1). Using the 18–30 formula for a 50-year-old will overestimate BMR by roughly 100 kcal/day. For a more accurate result, use an age-appropriate formula or a calculator that includes age brackets.

What does “activity factor” mean in plain terms?

It is a multiplier that estimates how many extra calories you burn beyond your resting metabolism. A factor of 1.2 means you burn 20% more than BMR; 1.9 means 90% more. It is a rough way to turn your daily activity into a number.

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in sex | Sex | Male=1, Female=0.9 | 1 | 0
in age | Age | years | 30 | 18
in weight | Weight | kg | 70 | 30
in act | Activity level | Sedentary=1.2, Light=1.375, Moderate=1.55, Active=1.725, Very active=1.9 | 1.55 | 0
out tdee | Total daily energy expenditure | kcal/day | (sex * (15.057 * weight + 692.2) + (1 - sex) * (14.818 * weight + 486.6)) * act | 0
out bmr | Basal metabolic rate | kcal/day | sex * (15.057 * weight + 692.2) + (1 - sex) * (14.818 * weight + 486.6) | 0