How fast you should lose weight is best expressed as a percentage of body weight per week, and the calculator offers three settings: 0.3%, 0.5% and 0.75%. For a 75 kg person that is roughly 0.23, 0.38 and 0.56 kg a week. Faster is possible on paper, but the one controlled comparison in lifters found that the slower of two rates preserved lean mass better in athletes — and the rate you can actually hold beats the rate that looks fastest.
Rates as a percentage of body weight
The calorie deficit calculator never asks "how many kilos a week?" It asks for a rate, and derives the kilos:
| Rate | Per week at 60 kg | At 75 kg | At 90 kg | At 110 kg | Daily deficit at 75 kg |
|---|---|---|---|---|---|
Conservative 0.3% | 0.18 kg | 0.23 kg | 0.27 kg | 0.33 kg | 248 kcal |
Moderate 0.5% | 0.30 kg | 0.38 kg | 0.45 kg | 0.55 kg | 413 kcal |
Aggressive 0.75% | 0.45 kg | 0.56 kg | 0.68 kg | 0.83 kg | 619 kcal |
The deficit column is weekly kg × 7,700 ÷ 7. Because the rate rides on current body weight, the same setting produces a gradually smaller deficit as the diet goes on. That is intended: a deficit that stayed fixed while you got lighter would become a larger and larger share of your expenditure.
The Zyra Nutrition FAQ describes the usual band as 0.25–0.75 kg per week and says that losing more than 1 kg a week "often involves muscle loss and is difficult to maintain long-term." The calculator's three settings sit inside that band for body weights up to about 100 kg; above that, the aggressive rate crosses 0.75 kg and the 35% cap starts to do work.
What faster costs
The clearest evidence we can cite is a randomised trial in 24 elite athletes who all kept four resistance sessions a week1. One group targeted a 0.7% loss of body weight per week; the other targeted 1.4%. Both groups lost about 5.5% of body weight, so the comparison is between two speeds to the same destination.
Slow group (target 0.7%/wk) | Fast group (target 1.4%/wk) | |
|---|---|---|
| Achieved rate | 0.7% per week | 1.0% per week |
| Time to lose ~5.5% | 8.5 weeks | 5.3 weeks |
| Energy intake cut by | 19% | 30% |
| Fat mass change | −31% | −21% |
| Lean body mass change | +2.1% | −0.2% |
Slow vs fast loss in 24 elite athletes who kept lifting · %
Slow (0.7% a week) Fast (1.4% a week target)
Source: Garthe et al. 20111. The slow group gained lean mass while losing fat; the fast group held lean mass flat and lost proportionally less fat. The authors' conclusion is that athletes who want to keep or gain lean mass and 1RM strength during a loss phase should aim for about 0.7% of body weight per week.
Read the limits honestly. This is one trial, small, in trained athletes with a supervised programme, and the fast group did not lose lean mass — it just did not gain any. It does not tell you what happens to an untrained person, or to anyone not lifting. What it does show is the shape of the trade: the faster rate cut intake by a third instead of a fifth, got there three weeks sooner, and gave up the lean-mass gain. Notice, too, that the trial's *slow* rate is close to the calculator's *aggressive* setting.
Beyond the trial, the costs of a faster rate are mechanical: a bigger deficit means less food to build protein and the fat floor out of, a higher protein target per kilogram (the calculator adds 0.2 g/kg on any loss goal), and more of the day spent hungry. None of that is an outcome claim; it is what a larger negative number does to the rest of the macro arithmetic.
In plain terms: faster gets you there sooner and asks more of you every day you are on the way.
What speed does outside the gym
Trials in people with obesity asked different questions and mostly compared much bigger gaps in speed.
Regain. The largest trial randomised 200 adults with obesity to a 12-week rapid programme or a 36-week gradual one, both aiming for 15% loss2. More of the rapid group reached at least 12.5% loss in the time allowed (81% vs 50%). After 144 weeks of maintenance, both had regained most of it: 71.2% vs 70.5% in completers, and 76.3% in both counting everyone randomised2. A smaller trial in 57 adults found the same: no difference in regain at 9 months3.
Share of lost weight regained by week 144, by rate of loss · %
Fat-free mass. In that smaller trial, the rapid group ate 500 kcal a day for 5 weeks and the slow group 1,250 kcal a day for 12. With similar total loss, the rapid group lost 8.8% of its fat-free mass against 1.3%, and fat-free mass loss was linked to later regain3. A 2022 review of 13 studies found faster loss may shed more fat-free mass and cut resting expenditure more during the losing phase, but that these differences shrank after 2 to 4 weeks of weight stability and did not change regain 9 to 33 months later4.
These rapid arms were very-low-energy diets, often supervised in hospital, far below the calculator's floors (1,500 kcal male / 1,200 kcal female) and its 35% cap. The calculator cannot produce them. They tell us about the direction of the trade, not about the three settings above.
In plain terms: across trials, speed did not decide who kept the weight off; very fast loss tended to take more fat-free mass with it while it lasted.
Choosing a rate you can hold
The rate that matters is the one you can sustain for the whole diet, because the weekly budget only works if most weeks actually land near it. Three practical checks:
- Look at the target, not the rate. If the aggressive rate puts the calorie target near the floor (
1,500 kcalmale /1,200 kcalfemale on the standard setting), the deficit is being cut short anyway and the moderate rate will produce almost the same number with less strain. The floors page has the arithmetic. - Match the rate to the training. Someone lifting hard with a specific strength goal has more reason to sit at
0.3–0.5%; someone with a lot to lose and no performance target can tolerate the higher end for a while, then step down. - Judge it on the trend, not the scale. Three to four weeks of trend weight tells you what rate you are really achieving. If it is well under the setting, expenditure or logging has drifted — see why weight loss stalls — and the fix is usually not a faster setting.
What the studies found
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Garthe et al., *Int J Sport Nutr Exerc Metab*1 | 24 elite athletes lifting 4 times a week; 0.7% vs 1.4% a week target | Slow group gained 2.1% lean mass; fast group unchanged (−0.2%) | 2011 |
| Purcell et al., *Lancet Diabetes Endocrinol*2 | 200 adults with obesity; 12-week rapid vs 36-week gradual programme | Regain after 144 weeks the same (71.2% vs 70.5% of lost weight) | 2014 |
| Vink et al., *Obesity*3 | 57 adults with overweight or obesity; 500 kcal/day for 5 weeks vs 1,250 kcal/day for 12 | Similar loss and regain; rapid group lost more fat-free mass (8.8% vs 1.3%) | 2016 |
| Fogarasi et al., *Curr Obes Rep*4 | Review of 13 studies with the same loss at different speeds | Faster loss may cost more fat-free mass while losing; differences fade after 2–4 weeks of stability | 2022 |
| Lowrie et al., *Obes Res Clin Pract*5 | Meta-analysis of randomised trials adding exercise to very-low-energy diets | Exercise kept about 0.83 kg more fat-free mass on average | 2025 |
Limits worth knowing
- One trial in lifters. The only rate comparison in people who lift is 24 elite athletes, and we could read only its abstract1.
- Different populations. The regain trials were in adults with obesity, mostly women in the largest one2.
- Extreme contrasts. The rapid arms were very-low-energy diets, not the calculator's aggressive setting.
- Fat-free mass is not muscle. DEXA and air-displacement measures include water, organs and bone.
- Abstracts only for every paper on this page.
Latest research
The newest study we read is a 2025 meta-analysis of randomised trials in adults with overweight or obesity on very-low-energy diets5. Across five trials (241 people), adding exercise kept more fat-free mass than the diet alone, by 0.83 kg on average (95% CI 0.17 to 1.49). The authors note few studies and risk of bias. It points the same way as the athlete trial: when loss is fast, training alongside it is what the fat-free-mass results depend on.
The short version
Speed is a percentage of body weight: 0.3%, 0.5% or 0.75% per week, which for 75 kg is about 0.23–0.56 kg. The one athlete trial that compared speeds found the slower rate (0.7%) preserved and added lean mass where the faster one did not1. Pick the rate you can hold, watch the trend for a month, and let the percentage shrink the deficit as you go.
- Speed did not change how much weight came back in two trials of adults with obesity23.
- Very fast loss took more fat-free mass while it lasted; the gap faded once weight was stable4.
- Exercise during fast loss kept more fat-free mass on average5.
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.
