Every calculator on the internet, including ours, is a guess. A good one, usually within 10–15%, but a guess. The problem is what most apps do next: they treat the guess as a fact and never revisit it.
Your expenditure is a moving target
Three things push your real energy needs around:
- Metabolic adaptation. After a few weeks in a deficit, expenditure drops 5–15% as the body economises. The target that worked in week one is now too high.
- Activity drift. People in a deficit unconsciously move less: fewer steps, less fidgeting. Wearables see it; formulas do not.
- Bodyweight itself. As you lose weight you burn less carrying it around.
The fix: adjust from the trend, not the formula
Log your intake honestly. Weigh in most mornings. After two weeks, compare the smoothed weight trend with what the deficit should have produced. Losing slower than planned? Your expenditure is lower than estimated, remove 100–150 kcal. Faster? Add them back.
This is the loop research nutritionists have used for decades and that MacroFactor made famous. Vitalume runs it every week, automatically, and (this is the part we care about) tells you why it changed the number.
Why the explanation matters
A silent adjustment feels like the app is guessing. “Your trend dropped 0.9 kg this week, above the 0.6 kg target, so I added 120 kcal, mostly carbs, on your training days” is something you can trust, argue with, or override. That transparency is the whole point of having a coach rather than a calculator.