Calculate your post-weigh-in rehydration plan for combat sports. Get fluid, electrolyte, and carb timing to maximize recovery before competition.
The hours between weigh-in and competition are critical for combat sport athletes who have cut weight. Rehydration isn't simply drinking as much water as possible — it requires a strategic protocol of fluids, electrolytes, and carbohydrates to restore blood volume, glycogen, and cellular hydration without causing gastrointestinal distress.
Research shows the body can absorb approximately 1–1.5 liters of fluid per hour under optimal conditions, meaning a 24-hour window allows recovery of 50–75% of lost water weight. The key is replacing not just water but also sodium (the primary electrolyte lost in sweat), potassium, and glycogen through carbohydrates.
This calculator provides an hour-by-hour rehydration protocol based on how much weight you cut, your rehydration window, and your sport. Follow it alongside guidance from your sports dietitian or physician. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Poor rehydration after weigh-in leads to impaired reaction time, reduced power output, increased injury risk, and poor performance. A structured protocol maximizes what your body can absorb in the available time window. Having a precise figure at your fingertips empowers better planning and more confident decisions. Manual calculations are error-prone and time-consuming; this tool delivers verified results in seconds so you can focus on strategy.
Water Lost = Walk-Around Weight − Weigh-In Weight Fluid Target = Water Lost × 150% (to account for ongoing losses) Max Absorption Rate: ~1–1.5 L/hour Sodium Target: 40–80 mmol/L in rehydration fluid (1–2g sodium per liter) Carbohydrate Target: 30–60g per hour for glycogen restoration Oral Rehydration Solution: • 1 liter water + 3/4 tsp salt + 6 tsp sugar • Or commercial sports drink + extra sodium Recovery Phases: Phase 1 (0–2 hrs): Sip fluids with electrolytes, 500–750 mL/hr Phase 2 (2–6 hrs): Increase to 750–1000 mL/hr, add small carb-rich meals Phase 3 (6+ hrs): Continue sipping, eat normal meals, monitor urine color
Result: 15 lbs (6.8 kg) to recover | ~10 L total fluid | 3–4g sodium/hr for first 6 hrs
You cut 15 lbs. Target fluid intake is 15 lbs × 150% = 10.2 liters over 24 hours. Phase 1 (hours 0–2): 1.5 L electrolyte solution (750 mL/hr). Phase 2 (hours 2–6): 4 L at ~1 L/hr with small meals every 2 hours (rice, bread, banana). Phase 3 (hours 6–24): 4.7 L at moderate pace with 3 regular meals. Expect to recover approximately 10–12 of the 15 lbs. Monitor urine color — target pale yellow by 12 hours pre-fight.
The intestinal absorption of water is driven by sodium-glucose cotransport in the small intestine. This is why oral rehydration solutions containing both sodium and glucose are absorbed 3–5x faster than plain water. The WHO oral rehydration solution (245 mOsm/L) is the gold standard, but commercial options like Pedialyte (250 mOsm/L) are nearly as effective.
The most common mistake is drinking too much plain water too fast. This causes bloating, nausea, and potentially dangerous hyponatremia (low blood sodium). The second mistake is eating a large, heavy meal immediately — your GI tract has been stressed by dehydration and needs gentle, frequent feeding rather than a feast. The third mistake is assuming body weight recovery equals full hydration — intracellular rehydration lags behind weight recovery.
The rehydration window fundamentally changes the strategy. With 24 hours, athletes can recover most of their weight through gradual, systematic rehydration. With 2-hour same-day weigh-ins, aggressive IV rehydration used to be common (now banned in many organizations). The trend in combat sports is toward same-day weigh-ins to discourage dangerous weight cuts, which is better for athlete safety.
With a 24-hour window, most fighters recover 10―15 lbs (5–7 kg) through aggressive rehydration and feeding. Some larger fighters have regained 20+ lbs. With a 2-hour window (same-day weigh-in), realistic recovery is only 3–5 lbs. Research shows athletes typically recover 50–75% of the weight they cut, depending on the time available.
Oral rehydration solutions (like Pedialyte or WHO-ORS formula) are optimal because they contain the ideal ratio of sodium, glucose, and water for maximum absorption. Sports drinks (Gatorade, Powerade) work but have less sodium and more sugar. Plain water is the worst choice because it dilutes blood sodium, triggers further urination, and creates a false sense of hydration.
Sodium is the primary electrolyte that determines how much water your body retains. Without adequate sodium, your kidneys will excrete much of the water you drink. Sodium also drives the thirst mechanism and enables glucose-sodium cotransport in the intestines, which is the fastest pathway for fluid absorption. Target 40–80 mmol of sodium per liter of fluid.
Not completely. While you can restore most blood volume and body weight within 24 hours, full cellular rehydration takes 48–72 hours. Studies show that cognitive function and fine motor control may not fully recover in 24 hours after large cuts (>8% body weight). This is one reason same-day weigh-ins have been proposed as a safety measure in combat sports.
Focus on high-carbohydrate, moderate-protein, low-fat, low-fiber meals. Good choices: white rice, pasta, bread, pancakes, bananas, honey, and lean protein (chicken, fish). Avoid high-fat foods (burgers, pizza, fried food), high-fiber foods (vegetables, whole grains), and spicy foods — they slow gastric emptying and can cause GI distress. Eat small meals every 2–3 hours rather than one large meal.
Monitor three indicators: (1) Urine color — pale yellow means adequate, dark means still dehydrated. (2) Body weight — weigh yourself periodically and compare to walk-around weight. (3) How you feel — headache, fatigue, and dark urine indicate continued dehydration. Having clear urine several times before competition is a good indicator of adequate hydration.