Maintenance After Weight Loss Calculator
Your maintenance falls when you lose weight — partly because a smaller body costs less to run, and partly through adaptation. The second part is much smaller than its reputation.
Your results
An estimate. The only reliable way to find your maintenance is to eat at a level for two weeks and compare weekly average weights.
The two components, and their real sizes
A smaller body costs less to run. Roughly 20–25 kcal per day per kilogram lost, before any adaptive effect. Lose 15 kg and that alone is around 330 kcal.
Adaptive thermogenesis is the part with the reputation. The measured figures are smaller than the folklore: in subjects who lost around 14 kg, adaptation was about 92 kcal/day below what body composition predicted immediately after weight loss, falling to about 38 kcal/day after four weeks of weight stabilisation. Roughly half of the initial figure reflected acute energy deficit rather than lasting change.
Which is why the calculator asks whether your weight has settled. Immediately post-diet the adaptive component is larger and partly transient.
What people actually experience as a 'broken metabolism'
38 kcal a day is an apple. It does not explain the common experience of regaining weight easily after a diet. Two things do:
- Reduced spontaneous movement. The largest and least visible component. In a deficit people unconsciously fidget less, walk less, take the lift. This is behavioural and it responds to deliberately restoring your step count.
- Under-reported intake. Well documented, largely unintentional, and it grows during and after a long diet.
Both are addressable, which is better news than a damaged metabolism would be. The practical steps are to raise calories deliberately over one to two weeks, restore your pre-diet activity level, and hold a weight range rather than a target for at least as long as the diet ran.
Common questions
Why is my maintenance lower after losing weight?
Mostly because a smaller body costs less to run — around 20–25 kcal per kg lost. A modest adaptive component adds to it.
Is metabolic damage real?
Not in the way it is usually meant. Adaptation settles at around 38 kcal/day. The larger effects are reduced daily movement and under-reported intake.
How long does adaptation last?
The acute portion resolves within weeks of weight stabilising. A modest residual persists.
How do I find my real maintenance?
Eat at your estimate for two weeks, weigh daily, and compare weekly averages. Adjust by 100–150 kcal.
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Track the numbers, not just calculate them
MyFitsy stores your weight, measurements and every session, so the figures above become a trend instead of a one-off.
