Fat loss · 6 min read
How Big Should Your Calorie Deficit Be?
Once you know your TDEE, fat loss comes down to eating below it. But how far below? Too small and progress stalls your patience; too large and you lose muscle, feel awful, and rebound. Here is how to pick a deficit that actually sticks.
The rule of thumb behind weight loss
A kilogram of body fat stores roughly 7,700 kcal (about 3,500 kcal per pound). So an average daily deficit of about 500 kcal adds up to roughly 3,500 a week, or close to half a kilogram of fat. This is a useful planning heuristic, not a law: water shifts, glycogen and your body adapting over time all make the scale bounce, which is why you judge progress on weekly averages, not single days.
Size your deficit as a percentage of TDEE, not a flat number
A flat -500 kcal means very different things to a 1,800 kcal person and a 3,000 kcal person. A percentage scales properly:
- Mild (about 10% below TDEE): slow, very sustainable, easiest to keep muscle. Great for lean people with little to lose.
- Moderate (about 20% below TDEE): the sweet spot for most people. Noticeable progress without misery.
- Aggressive (about 25 to 30% below TDEE): fast, but harder to sustain, hungrier, and riskier for muscle. Best kept short and paired with high protein.
Worked example (TDEE 2,400 kcal). Mild = ~2,160. Moderate = ~1,920. Aggressive = ~1,700. The moderate option costs about 480 kcal a day, which lines up with roughly 0.45 kg of loss per week.
Why a smaller deficit often wins
Bigger is not better. As you diet, your body lowers its energy use (partly a real metabolic effect, partly because you move less without noticing). A gentler deficit:
- preserves more muscle, which keeps your metabolism and your physique better;
- leaves room to cut further later when progress slows, instead of starting with nowhere to go;
- is simply easier to stick to, and adherence beats theoretical speed every time.
Set a floor and reassess
Avoid dropping for long stretches below your BMR. Recalculate your TDEE after every 4 to 5 kg of weight change, because the number that was right at the start will be too high once you are lighter. If the scale average has not moved in two to three weeks, that is your signal to trim a little more or add activity, not to crash.
The calculator estimates your TDEE and suggests cutting calories alongside maintenance and bulking, so you can pick a deficit with the numbers in front of you.
Find your TDEE and a deficit target →Frequently asked questions
Is a 500 calorie deficit good?
For many people, yes. It is close to a 20% deficit at a typical TDEE and tends to produce around 0.45 kg of loss per week, which is sustainable. If your TDEE is low, 500 may be too aggressive; size it as a percentage instead.
How fast is it safe to lose weight?
A common guideline is about 0.5 to 1% of body weight per week. Faster than that raises the risk of muscle loss and is harder to maintain, though people with more fat to lose can tolerate the upper end better.
Why has my weight loss stalled in a deficit?
Usually one of three things: your TDEE has fallen as you got lighter and through adaptation, your intake has crept up, or you are retaining water. Recalculate your TDEE, tighten tracking for two weeks, and judge by the weekly average before changing anything.
Should I eat back exercise calories?
If your activity multiplier already accounts for your training, do not also eat back what a tracker says you burned, or you will erase the deficit. Pick one accounting method and stick with it.
References
- Trexler ET, Smith-Ryan AE, Norton LE. Metabolic adaptation to weight loss: implications for the athlete. J Int Soc Sports Nutr. 2014;11:7. doi:10.1186/1550-2783-11-7
- Hall KD, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837. doi:10.1016/S0140-6736(11)60812-X
- Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation. J Int Soc Sports Nutr. 2014;11:20. doi:10.1186/1550-2783-11-20