Fight Weight Cut Calculator

Plug in your current weight, your weigh-in target, and how many days you have. This tool splits the cut into a gradual fat-loss phase and a final water-cut phase, flags whether the water cut stays inside the 5–8% body-weight ceiling that sports-medicine research recommends, and gives you a post-weigh-in rehydration target. All math runs in your browser — nothing is sent anywhere.

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The dropdown lists standard MMA (unified rules) weigh-in limits. For BJJ/IBJJF divisions — which are measured with the gi and vary by ruleset — enter your division's published limit in the target field directly.

Enter a current weight, a target weight, and days until weigh-in to see your plan.

How this calculator works

Every number here is pulled from the sources cited in our full guide, How to Cut Weight Safely for MMA or BJJ Competition. Nothing is invented:

  • Fat-loss phase. We reserve the final 7 days for the water cut, then spread the rest of the drop across the weeks before it at 1–2 lbs per week — the rate the International Society of Sports Nutrition (2022) links to preserving muscle, via a 500–750 kcal/day deficit.
  • Water cut. Whatever the fat-loss phase can't cover becomes the acute water cut. The American College of Sports Medicine (2023) and our guide cap water manipulation at 5–8% of body weight.
  • Safety verdict. Green keeps the required water cut at or under ~5%. Yellow lands in the 5–8% band. Red exceeds 8%, and any cut past 10% is flagged high-risk — the level the British Journal of Sports Medicine (2022) ties to impaired reaction time, power output, and injury resilience.
  • Rehydration. The fluid target is 150% of the water you lose, the ACSM figure for replacing fluid within 4–6 hours after weigh-in.

The verdict is driven by the water-cut percentage — the acute, risky portion — not the total drop, because losing weight gradually through fat loss over weeks is far safer than pulling it off in the final days through dehydration.

Not medical advice. Weight cutting carries real health risks, including heat stroke, cardiac and kidney complications, and death when done aggressively. This calculator is an educational estimate, not a prescription. Consult a qualified sports medicine professional before attempting any weight cut, especially your first one.

Sources: American College of Sports Medicine (2023); British Journal of Sports Medicine (2022); International Society of Sports Nutrition (2022), as cited in our weight-cutting guide. See also our companion piece on fighter nutrition for weight cutting.