Find Your Real Maintenance Calories With a Two-Week Test

Every calorie calculator hands you a number with false confidence. Two people with the same age, height, weight and job can differ in daily energy burn by several hundred calories, and no formula can see that coming. The good news is that you can check the estimate against your own body in two weeks, using nothing but a kitchen scale, a food log and a bathroom scale. Here is the procedure, with an example person to make the arithmetic concrete.

Step 1: Get a starting estimate

Total daily energy expenditure (TDEE) is your resting burn multiplied by an activity factor. For the resting part, the Mifflin-St Jeor equation, published in 1990, is the most widely used:

BMR (men) = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5

BMR (women) = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161

Our example person, Jordan, is a made-up 29-year-old man, 170 cm tall, 72 kg. His BMR comes out as 10 x 72 + 6.25 x 170 - 5 x 29 + 5 = 1,642.5 calories. You can skip the manual work and use the BMR calculator, but it helps to see that the formula is only four terms.

Step 2: Pick an activity factor, and be honest

The usual multipliers are 1.2 for desk work with no exercise, 1.375 for light exercise one to three days a week, 1.55 for moderate exercise three to five days, 1.725 for hard training most days, and 1.9 for very physical work plus training. Most people choose one level too high, because they remember their best week, not their average one.

Jordan works at a desk and runs twice a week. He picks 1.375. That gives 1,642.5 x 1.375 = about 2,258 calories. Had he picked 1.55 for "moderate", his estimate would be 2,546, a gap of nearly 300 calories a day from one dropdown choice. This is the biggest source of error in the whole exercise, and the reason for the test.

Step 3: Log everything for 14 days

Weigh your food where you can, and record drinks, oil, sauces and the handful of nuts you ate while cooking. Do not change how you normally eat, since you are measuring your life, not an ideal week. A few ground rules:

• Weigh yourself every morning after the bathroom, before eating, in similar clothing
• Keep eating roughly the same amount each day, with weekends included
• Skip the first two or three days of data if you changed your routine to start logging
• If a day is a complete guess, such as a wedding dinner, mark it and leave it out of the average

Step 4: Average the scale, not single days

A single morning weigh-in can swing by a kilogram or more because of water, salt, digestion and hormones. One kilogram of that noise, treated as real tissue, would mean about 550 calories a day of phantom surplus or deficit over 14 days. So compare averages: take the mean of the first seven mornings and the mean of the last seven.

Say Jordan logs an average of 2,300 calories a day. His first-week average weight is 72.3 kg and his second-week average is 72.0 kg, so he lost 0.3 kg over the stretch.

Step 5: Do the arithmetic

Maintenance = average intake + (kg lost x 7,700) / days

The 7,700 figure is the commonly used estimate of energy in a kilogram of body-weight change (the older pounds version is 3,500 per lb). It is an approximation, since body weight is not pure fat, but it is fine for a short test. For Jordan: 0.3 x 7,700 = 2,310 calories spread over 14 days is 165 a day. Add that to his intake: 2,300 + 165 = about 2,465 calories. If he had gained weight instead, you subtract the daily surplus.

So his measured maintenance is roughly 2,465, against the calculator's 2,258. The calculator was about 200 low, which is well within normal person-to-person variation.

What can ruin the result

• Under-reporting intake. People who log honestly still tend to miss 10 to 20 percent of what they eat, especially cooking oil and liquid calories. If your log says 1,800 and you are not losing weight, the log is more likely wrong than your metabolism.
• Two weeks is short. Water retention after a salty meal or a hard workout can mask real changes. If the numbers look odd, extend to four weeks.
• Starting a diet or new workout mid-test. Metabolism adapts, and glycogen stores shift quickly, which shows up as fast early weight change.
• Menstrual cycle effects. For people who menstruate, water weight can move a kilogram or more across a cycle, so a test that spans a full cycle gives a cleaner reading.

Using the number

Once you have a tested maintenance level, adjusting is simple. Modest deficits, in the range of 10 to 20 percent below maintenance, are easier to sustain than aggressive ones. For Jordan that is roughly 2,000 to 2,200 calories a day. Adjust after two or three weeks of trend data, not after a single bad weigh-in. The calorie calculator and the TDEE calculator give you a starting figure, and the macro calculator can divide a target into protein, carbohydrate and fat.

This process is general information for healthy adults. If you have a medical condition, take medication that affects weight, are pregnant, or have a history of disordered eating, check with a doctor or dietitian before making changes based on calorie math.