Post Weigh-In Rehydration Calculator
Estimate how much fluid and sodium to take in after a weight-cut weigh-in to rehydrate before you compete.
How it works
Fluid to replace ≈ 1.5 × fluid lost · Per hour = total ÷ hours to compete · Sodium ≈ 1 g per litre
After a water cut you need to replace more than you lost — about 150% — because some fluid is passed as urine before it can be retained. Sodium and carbohydrate taken with the fluid help you hold onto it and refill muscle glycogen, so the guideline pairs volume with electrolytes rather than plain water. Spreading intake evenly across the hours before competing is far more effective, and safer, than gulping large volumes at once.
Worked example
Losing 3 kg (≈3 L) with 20 hours to compete: replace 1.5 × 3 = 4.5 L, which is 4.5 ÷ 20 ≈ 0.23 L/hr, alongside roughly 4.5 g of sodium spread through the day.
Frequently asked questions
Why drink more than I lost?
Rehydration is inefficient — a portion of plain fluid is lost as urine before your body retains it. Aiming for about 150% of losses, taken with sodium and carbohydrate, helps you actually restore the fluid rather than pass it straight through.
Can I just drink water fast?
No. Rapid plain-water intake is both ineffective and dangerous — it can dilute blood sodium (hyponatraemia). Include electrolytes and carbohydrate, sip steadily, and rehydrate under supervision.
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Rapid weight manipulation carries real health risks. This is an educational estimate only — cut and rehydrate under medical or qualified coaching supervision, never alone.