A calorie deficit should be sized from a rate of weight change as a percentage of body weight, not picked as a round number. That is how the calorie deficit calculator works: you choose a rate, it converts the rate into calories, and then two guardrails — a cap and a floor — decide whether the raw number stands. The answer for a 75 kg person is roughly 250, 400 or 600 kcal per day depending on the rate, and the rest of this page shows exactly where those figures come from.
This is arithmetic, not a trial result. The constants are the ones the calculator and MacroDiet share; none of them is a law of physiology.
A deficit from a rate, not a round number
A calorie deficit is the gap between what you eat and what you expend. The internet's favourite number for it is 500 kcal a day. The problem with a fixed number is that it means very different things to different bodies: 500 kcal is a gentle nudge for someone at 130 kg and a hard cut for someone at 55 kg.
Setting the deficit as a rate fixes that. The calculator asks for one of three rates, each a fraction of current body weight per week, and runs two lines of arithmetic:
weekly loss (kg) = body weight (kg) × ratedaily deficit (kcal) = weekly loss × 7,700 ÷ 7
The 7,700 kcal per kg is the planning value for the energy in a kilogram of body fat. It is a rounded convention, not a measurement of you — see why 7,700 is a planning number. Multiplying by 7,700 ÷ 7 = 1,100 turns kilograms per week straight into calories per day.
In plain terms: the deficit is *derived* from how fast you want the trend to move, and it shrinks automatically as you get lighter.
The three rates
| Rate setting | Percent of body weight per week | At 60 kg | At 75 kg | At 90 kg | At 110 kg |
|---|---|---|---|---|---|
| Conservative | 0.3% | 198 kcal | 248 kcal | 297 kcal | 363 kcal |
| Moderate (default) | 0.5% | 330 kcal | 413 kcal | 495 kcal | 605 kcal |
| Aggressive | 0.75% | 495 kcal | 619 kcal | 743 kcal | 908 kcal |
Every cell is weight × rate × 1,100, rounded. Two things stand out. First, the aggressive rate at 110 kg is bigger than the conservative rate at 60 kg by more than four to one — a fixed number could never represent both. Second, the rates are deliberately modest: even "aggressive" is three quarters of a percent a week, which for the 75 kg example is a little over half a kilogram.
The faster rate is not free. It comes with more hunger, less energy for training, and a bigger protein requirement per kilogram (the calculator adds 0.2 g/kg to the protein target on any loss goal). The default is moderate for a reason; the rate page goes through what each speed costs.
The 35% cap and why
After the deficit is computed, the calculator compares it with 35% of your TDEE (total daily energy expenditure — everything you expend in a day). Whichever is smaller wins:
max deficit = TDEE × 0.35deficit = min(raw deficit, max deficit)
The cap matters for heavier people with a low activity multiplier, because the rate scales with body weight while TDEE does not scale as fast. Take a 120 kg, 180 cm, 45-year-old male profile on the sedentary setting: Mifflin-St Jeor BMR is 2,105 kcal, the multiplier is 1.15, so TDEE is 2,421 kcal. The aggressive rate asks for 0.9 kg a week, which is 990 kcal a day — 41% of TDEE. The cap trims it to 847 kcal and the target lands at 1,574 kcal.
Why 35 percent? Past roughly a third of expenditure, the target starts to squeeze protein and the fat floor at the same time, and the day gets hard to build out of real food. The cap is a design choice that keeps the output inside a range the rest of the macro rules can still satisfy.
The floors
The last check is a hard floor on the calorie target itself, applied only on a loss goal:
| Floor setting | Male | Female |
|---|---|---|
| Standard | 1,500 kcal | 1,200 kcal |
| Lower | 1,200 kcal | 1,000 kcal |
If the computed target is below the floor, the target becomes the floor and the calculator flags it. That means the *effective* deficit is smaller than the one you asked for — the floor takes priority over the rate. Why calculators stop at 1,200 or 1,500 covers what happens in that case and why the "lower" setting exists.
Worked example (75 kg)
Profile: female, 75 kg, 168 cm, 35 years, trains 4–6 times a week, moderate day-to-day activity.
- BMR (Mifflin-St Jeor):
10 × 75 + 6.25 × 168 − 5 × 35 − 161 = 1,464 kcal. - TDEE: multiplier
1.55 + 0 = 1.55, so1,464 × 1.55 = 2,269 kcal. - Cap:
2,269 × 0.35 = 794 kcal— the largest deficit allowed. - Deficit and target at each rate:
| Rate | Weekly loss | Daily deficit | Capped? | Target | Below floor (1,200)? |
|---|---|---|---|---|---|
Conservative 0.3% | 0.225 kg | 248 kcal | no | 2,022 kcal | no |
Moderate 0.5% | 0.375 kg | 413 kcal | no | 1,857 kcal | no |
Aggressive 0.75% | 0.563 kg | 619 kcal | no | 1,650 kcal | no |
Neither guardrail fires here — this profile has enough expenditure headroom for all three rates. Change the profile to 55 kg, 160 cm, sedentary, and all three targets fall under the 1,200 floor; the floors page walks that case.
Type the same profile into the calorie deficit calculator and you will get the same rows; the calorie calculator shows the BMR and TDEE steps on their own.
The short version
A deficit is a rate first and a number second. Pick 0.3%, 0.5% or 0.75% of body weight per week; multiply by 1,100 to get calories per day; cap it at 35% of TDEE; never let the target fall through the floor. For 75 kg that is about 248 / 413 / 619 kcal. Re-run it every couple of weeks, because the number is supposed to shrink as you do.
Educational overview only — not medical advice. Zyra is a training and nutrition tracking tool; the rates, caps and floors on this page describe how the calculator behaves, not what any individual should do.