Your estimated energy expenditure is a deterministic calculation based on your calorie intake and change in trend weight.
We start with the basic energy balance equation: Calories in - Calories out = Change in stored energy (and changes in stored energy obviously come with changes in weight over time). Since we want to estimate your energy expenditure, we need to rearrange the equation to solve for "Calories out": Calories in - Change in stored energy = Calories out.
"Calories in" is simple to calculate, since you're either logging your food in MacroFactor, or importing nutrition information from another source that's synced with this app. "Change in stored energy" is slightly tougher to estimate, since we're ultimately working with weight data. However, we can use information about your rate of weight change and the caloric content of fat tissue versus lean tissue to estimate the change in stored energy associated with your changes in weight (fat has a greater energy density than lean mass; at slower rates of weight loss or faster rates of weight gain, we anticipate that a larger proportion of the weight you gained or lost came from fat mass). From there, it's simply a matter of solving the equation.
For example, if we estimate that you've been in an energy surplus of 200 Calories per day based on the rate at which your trend weight has been changing, and we can see that you've been eating approximately 3000 Calories per day, we can calculate that your daily energy expenditure is approximately 3000 - 200 = 2800 Calories.
As you continue to use MacroFactor, we'll continue monitoring your energy intake and changes in weight to update your calculated energy expenditure. If you gain or lose a substantial amount of weight, or if your activity levels change, we won't have to guess how those changes will impact your daily energy expenditure; we'll be able to measure the impact, and adjust your calorie and macro recommendations accordingly.
Since our calculation of your energy expenditure is based solely on tracked energy intake and changes in weight, that allows our calorie and macro adjustments and recommendations to be "adherence-neutral." In other words, you don't have to be a robot with perfect dietary adherence for MacroFactor to make appropriate updates to your calorie and macro recommendations, based on your goals. If you eat a little more or a little less one week than your macro program recommended, that's totally fine! Your updated calorie and macro recommendations for the next week are based on your actual energy intake and changes in weight, not how well you stuck to our recommendations. Not only does this allow our systems to be more robust to deviations from your macro program (which are totally fine; we don't expect people to be robots), but we also hope that this "adherence-neutral" system will make deviations from your macro program less psychologically stressful. Since our system doesn't require or expect perfect dietary adherence to make appropriate updates to your calorie and macro targets, that should lessen the perceived psychological cost of occasionally deviating from your recommended calorie targets.
As one final note, this calculation of energy expenditure is really at the heart of MacroFactor, and a lot of work has gone into ensuring that it's as accurate and reliable as possible, given what we know about human physiology and metabolism. We've also taken great care to make it as robust as possible to less-than-perfect tracking (the more consistently you track your weight and nutrition, the better our recommendations will be, but if you occasionally forget to log your weight or nutrition, our algorithms still do an admirable job of rolling with the punches). However, it has one Achilles heel: partial nutrition tracking. If, for example, you track your breakfast and lunch one day, but you don't put your dinner in the Food Log, we have no way of knowing that your energy intake for the day is incorrect, and your estimated daily energy expenditure (and future calorie recommendations) will decrease accordingly. However, as long as you avoid partial nutrition tracking, we should be able to accurately and reliably estimate your energy expenditure, and therefore recommend and appropriately adjust calorie and macro targets for you based on your goals.
If you'd like to read more about how the expenditure calculation works, you may enjoy this article from the website. You might also enjoy this knowledge base article about interpreting changes to your expenditure. Finally, you might also enjoy this article discussing why MacroFactor doesn't need data about energy expenditure during exercise to accurately estimate your total energy needs.