Your energy expenditure is the total number of calories your body burns in a day. It includes the energy you use at rest, digesting food, moving around during your day, and exercising. It is often referred to as your TDEE (total daily energy expenditure).
Expenditure is the foundation of your nutrition plan. Once MacrosFirst knows how much you burn, it can set targets that move you toward your goal at the rate you chose. This article explains where your starting expenditure comes from, how MacrosFirst learns your real expenditure from your own data, and why it moves the way it does. For the big picture of how expenditure fits with your goal and plan, see How MacrosFirst Sets Your Targets.
Before you've logged anything, MacrosFirst needs a sensible place to start. Rather than a generic calculator formula, your starting expenditure estimate is built on the doubly labeled water method, the gold standard for measuring how many calories people actually burn in everyday life, outside of a lab, combined with validated physical activity modifiers. For those with very lean, muscular builds, MacrosFirst will use your body fat percentage to further adjust the estimate since muscle burns more energy than a typical body of the same weight.
This is a good starting point, but it describes an average person who looks like you on paper. Real people with the same stats can burn hundreds of calories more or less. That's why MacrosFirst doesn't stop here.
The idea behind MacrosFirst’s dynamically updating energy expenditure algorithm is simple energy balance. If you eat more than you burn, your weight trends up. If you eat less, it trends down. If you eat about what you burn, it holds steady. So by watching two things you're already tracking, your calorie intake from your food log and the direction of your weight trend from your weigh-ins, MacrosFirst can work backward to what you actually burn.
For example, if your weight trend is flat while you eat about 2,400 calories a day, you're burning about 2,400. If you eat 2,000 a day and your trend is dropping, you're burning more than 2,000, and the speed of the drop tells MacrosFirst how much more.
There's one subtlety that makes this harder than it sounds: how many calories a pound (or kilo) of weight change represents isn't a fixed number. It depends on how much of that change is fat and how much is lean tissue, which in turn depends on your body composition. MacrosFirst accounts for this using models from metabolism research and data from CALERIE, a two-year controlled study of calorie restriction.
Your expenditure moves through three phases. It begins with the starting estimate, the science-based estimate built on population averages described above. Once you've logged enough food and weigh-ins, it starts updating, learning from your data each time you weigh in. If recent calorie intake or weigh-in data is not available, say due to a break in logging, it holds where it is rather than guessing, and picks back up once you resume logging. On your expenditure chart, these days are labeled Exp. updating and Exp. holding.
To update expenditure, MacrosFirst needs:
Food logged on at least 3 of the past 7 days, and
At least 2 weigh-ins in the past 14 days
This is the minimum MacrosFirst needs to model your expenditure. The more consistently you log and weigh in, the sharper the model becomes for you. Today's food doesn't count until the day is over, since you're probably still logging.
Your expenditure moves forward on the days you weigh in. In between weigh-ins it holds, and when you weigh in next, MacrosFirst goes back and recalculates the days in between using the food you logged on them. For the full details, see What Data MacrosFirst Needs to Update Your Targets.
You might notice your expenditure moves slowly, even after a big day or a big swing on the scale. That's deliberate.
Day-to-day weight jumps around with water, salt, carbs, and digestion, and one high-calorie day doesn't change your metabolism. Research on estimating energy intake from weight change shows it takes weeks of data, not days, to see a reliable signal through that noise. So each update moves your expenditure a small step toward what your latest data suggests. Real changes show up within a few weeks, while one-off noise doesn't push your targets around.
Smartwatches and fitness trackers are good at some things, but estimating calories burned isn't one of them, and the research on this is remarkably consistent.
In a Stanford study of seven popular wrist-worn trackers worn by 60 people, heart rate was mostly accurate, but none of the devices measured calories burned accurately. Even the best was off by an average of 27%, and the worst by 93%. A review of 158 studies across nine wearable brands reached the same conclusion: steps were measured accurately, but no brand measured energy expenditure accurately. A 2023 study found that newer devices haven't solved it either. The Apple Watch 6, Polar Vantage V, and Fitbit Sense all showed poor calorie accuracy across walking, running, cycling, resistance training, and sitting.
Worse, the error isn't consistent. It varies by person, by device, and by activity, so you can't simply correct for it. Your food log and your scale, on the other hand, reflect what actually happened to your body.
We don't use your wearable's calorie burn estimates. However, if you sync or log your steps, a noticeable change in your usual step count can nudge your expenditure slightly, but your food log and weight trend do the real work.
We didn't make this up. Our approach was developed with guidance from a metabolism scientist formerly at the National Institutes of Health (NIH), and every core piece comes from published, peer-reviewed research. On top of that foundation, we've added our own refinements for real-world logging, like how to handle days you skip, weigh-ins that bounce around, and breaks in your data.
Now that you know how MacrosFirst measures your expenditure, these articles cover what to do with it:
"What am I looking at on the expenditure chart?" Reading Your Expenditure Chart
"How does my expenditure turn into weight gain or loss?" Energy Balance
"How much do I need to log for it to keep updating?" What Data MacrosFirst Needs
"How do I change my starting estimate, activity level, or start date?" Expenditure Settings
What am I looking at on my expenditure chart? Seeing your own expenditure over time is the best way to make everything in this article click, from your starting estimate to the days it holds and updates: Reading Your Expenditure Chart.
