How much weight can you actually lose in a week?

Five percent is the figure with real evidence behind it. What that evidence measured is much narrower than the way the number gets quoted, and the gap between the two is where fighters get hurt.

This is the question I get more than any other, usually by message, usually with a number attached and a date that is too close. And it does have an answer.

Just not a single one.

Because the honest version depends on three things: what you are actually removing, how long you get to put it back, and what you are willing to pay for it.

The 5 percent finding

A meta-analysis published in 2022 pooled the studies on rapid weight loss in Olympic combat athletes and reached a clear conclusion.

Losing up to 5% of body mass in under 7 days produced no measurable effect on power or strength performance.

This rate is one of the few things in weight management that holds across sports. Where the rest of it does not, and why, is set out for one very different population in jockeys.

That is a real result from a proper review, and it is the reason 5 percent has become the working ceiling in serious practice.

Now read what it says again, closely. It measured power and strength. In a laboratory. Not fight-night output across 12 rounds, not decision-making in the tenth, not what a chin does when the brain has less fluid around it.

And it says nothing at all about what the week cost the rest of you.

What is actually coming off

A week removes four different substances, and they have completely different costs.

• Gut content. Reduce fibre and food volume and the digestive tract empties. Fast, painless, and worth a surprising amount on the scale.
• Glycogen and the water bound to it. Every gram of stored carbohydrate holds roughly three of water. Empty the stores and both go. This is the single biggest fast mover in the week, and it also happens to be your fuel.
• Fat. Real, and slow. Even a hard deficit removes somewhere around half a kilo to a kilo of genuine fat tissue in 7 days, which on a 70 kg frame is roughly 1 percent of body mass. Anyone promising several kilos of fat in a week is describing the two categories above and calling it something else.
• Water beyond that. The dangerous portion.

The first three are unpleasant. The fourth is where medical risk lives, and it is the one that most cuts lean on hardest, because it is the only one that moves fast enough to save a badly planned camp.

Your weigh-in format changes the answer more than your discipline does

This is the part almost nobody accounts for.

A survey of UK combat athletes split them by weigh-in timing, and the difference was stark. Athletes weighing in 24 hours or more before competing reported a habitual loss of 9.7% of body mass.

Athletes with a weigh-in under 24 hours out reported 5.2%.

The highest figures each group had ever cut: 13.0% against 8.7%.

Same sports. Same athletes, more or less. The recovery window decided how far they were prepared to go, which tells you the size of a cut is a response to the rules, not a property of the fighter.

So the first question to ask is when you step on the scale relative to the bell, and how much you can lose comes second, because timing determines whether anything you take out can go back in.

What people actually do

Reported practice sits well above what the research supports. Across the Olympic combat sports the typical figure sits around 5% of body mass. In mixed martial arts and muay thai it runs considerably higher, and documented ranges across all of it reach 12% and beyond.

Two mixed martial arts cohorts in a systematic review lost an average of 7.4 kg, close to 10% of body mass, then put 11.7% back on in the window after the scale.

Note the direction of that second number. They regained more than they lost, which is the point of the exercise as it is currently played.

So what is the answer

For a healthy adult male with a full recovery window, 5 percent of body mass in a week is the line where the evidence still holds. On 70 kg that is 3.5 kilograms.

On 84 kg, just over four.

The most common place that ceiling gets tested is a bout accepted at short notice. What the arithmetic actually permits in one, 2 or 4 weeks is set out in short notice.

Below that line you are inside what has been studied. Above it you are in territory where performance data thins out and the medical risk does not.

Three things narrow it further.

A short recovery window. With a fight-day weigh-in the safe figure roughly halves, because nothing you remove gets meaningfully replaced.

Female physiology. Lower total body water means the same percentage represents a larger share of the fluid you have. The range is tighter, and the evidence base is thinner.

Age under 18. Nothing in the research above was measured on a growing athlete, and none of it applies to weight cutting under 18.

Our calculator works out the range for your own weight, sex and weigh-in format in about 30 seconds. It exists because this is arithmetic, and arithmetic is easier to argue with than a coach's opinion.

The same answer as a table

The percentage is easier to act on when you have already done the arithmetic, so here it is done.

The acute reduction ceiling depends on how close to the weigh-in you start. The 2025 ISSN position stand on combat sports puts numbers on it: suitable losses in body mass of 6.7 percent in the final 72 hours before the weigh-in, 5.7 percent in the final 48, and 4.4 percent in the final 24. A same-day weigh-in needs a much smaller figure, because nothing you remove gets meaningfully replaced before you compete.

The same-day column is this site's working ceiling of about 2.5 percent. It is not a figure from the position stand.

The 5 percent figure above and the graded figures here are answering slightly different questions. Five percent is the general line for a week where recovery is not the constraint. The graded numbers are more precise once you know how many hours you actually have, which is why 5 percent on 70 kg, 3.5 kilograms, sits between the 24 and 48 hour columns.

All figures in kilograms, and all of them ceilings rather than targets. A ceiling is the point past which the published evidence stops supporting you. It is not a plan, and a fighter who lands on the ceiling every camp is telling you something about his division rather than about his discipline.

Three qualifications sit on top of the whole table. Female athletes have a tighter range for the reasons set out below. Nobody under 18 belongs anywhere in it. And the numbers assume a healthy adult arriving at the cut in normal condition, not one who is ill, injured or already depleted.

The calculator works the range out for your own weight, sex and weigh-in format.

If the number does not fit

Sometimes you run it and the gap is bigger than the range. That is not a failure of will, and no amount of discipline closes it safely.

If it never fits, the problem is upstream of the cut. Which division you belong in has the band.

There are three honest responses. Move up a division. Take the fight at a catchweight. Withdraw and plan the next one properly, with a real runway.

What none of them is: pushing on and finding out what happens when you miss.

None of them is a protocol, a supplement or a trick, and every fighter I have said this to already knew it before I opened my mouth.

The bit I would put on the wall

And the size of the gap itself was set long before camp began, in the weeks nobody plans.

Every figure on this page describes what a body will tolerate once. None of them describes what it tolerates 8 times a year for a decade.

The literature on that is a different and much less comfortable body of work, and it is the reason I keep pushing camps toward starting closer to the weight rather than getting better at removing it.

The food side of the whole cut, phase by phase from base camp to the scale, is in the weight cut meal plan.

Common questions

How much weight can you lose in a week?

For a healthy adult male with a full recovery window, 5 percent of body mass in under 7 days is where the evidence still holds. On 70 kg that is 3.5 kilograms, on 84 kg just over four. Above that line the performance data thins out while the medical risk does not.

How many kilos can you lose in a week?

Roughly 3.5 kilograms at 70 kg and a little over four at 84 kg, if the 5 percent ceiling is applied and there is a full window to recover afterwards. The figure scales with body mass rather than being a fixed number of kilos.

What did the 5 percent research actually measure?

Strength and power, neither of which dropped measurably. That is much narrower than the way the number is usually quoted. The same 5 percent has been shown to impair kidney function, which the strength result says nothing about.

Does the weigh-in format change how much you can lose?

More than the discipline does. What decides the safe figure is the gap between the scale and the first bout, because that gap is what determines how much of the loss can be put back before competing.

What if you need to lose more than 5 percent?

That is the point at which the division, rather than the diet, is the thing to reconsider. Where the loss is forced by a bout accepted at short notice, the arithmetic of what one, 2 or 4 weeks actually permits is a separate calculation.