Calculate calorie, carbohydrate, sodium, and fluid needs for ultra marathon races. Plan nutrition by distance, pace, body weight, and conditions.
The Ultra Marathon Nutrition Calculator estimates your calorie, carbohydrate, sodium, and fluid requirements for ultra-distance races. Getting nutrition right is one of the biggest challenges in ultra running — GI distress is the leading cause of DNF (did not finish) in 100-mile races, and even mild nutrition errors compound over hours of racing.
This calculator accounts for your body weight, target pace, race distance, and environmental conditions to generate a comprehensive fueling plan. It covers standard ultra distances from 50K through 200 miles and provides hourly intake targets that you can map to specific food and drink choices.
Whether you're planning your first 50K or pacing a 100-miler, a data-driven nutrition plan dramatically improves your chances of finishing strong. Practice every element of your plan in training — race day is not the time to experiment. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation.
Ultrarunning nutrition is more complex than shorter-distance racing because the body's ability to absorb calories decreases over time while energy demands remain high. Runners need to balance intake of carbohydrates, electrolytes, and fluids while managing a GI tract under stress. This calculator provides evidence-based targets that form the foundation of a race nutrition plan.
Calorie Expenditure: • Approx. 80–110 cal/mile for most runners (varies by weight and terrain) • Hourly burn = cal/mile × miles/hour Intake Targets (per hour): • Calories: 200–400 cal/hr (30–50% of expenditure) • Carbohydrates: 60–90 g/hr (mix glucose + fructose for max absorption) • Sodium: 500–1000 mg/hr (higher in heat/humidity) • Fluid: 400–800 mL/hr (adjusted for sweat rate and conditions) GI Tolerance Factor: • Early race: can absorb closer to 90 g/hr carbs • Late race (12+ hrs): may tolerate only 40–60 g/hr
Result: Cal: ~275/hr | Carbs: ~70g/hr | Sodium: ~700mg/hr | Fluid: ~600mL/hr
A 160 lb runner at 15:00/mile pace covers 4 miles/hour and burns approximately 380 cal/hr. Targeting 70% caloric replacement gives ~275 cal/hr. At 4 cal/g carbohydrate, 70g carbs provides 280 cal. Sodium need at moderate temps is approximately 700 mg/hr. Over a 25-hour 100-mile race, total intake targets: ~6,875 cal, ~1,750g carbs, ~17,500mg sodium, and ~15 liters of fluid.
Start by calculating hourly targets from this calculator, then map those targets to specific products and foods. For example, if your target is 275 cal/hr and 700 mg sodium/hr, one plan might be: 1 gel (100 cal, 200 mg Na) + 500 mL sports drink (100 cal, 300 mg Na) + 1 salt capsule (200 mg Na) + half a banana (50 cal) + pretzels (25 cal). Write out what you'll consume at each aid station.
The most frequent ultra nutrition errors are: (1) Not eating enough early in the race when the gut is fresh, creating a caloric deficit that's impossible to recover later. (2) Relying on a single food type that becomes intolerable at hour 10+. (3) Drinking too much water without electrolytes, risking hyponatremia. (4) Ignoring thirst or hunger cues until severe symptoms appear. (5) Eating too much fiber or fat, which slow gastric emptying.
The gut is highly trainable. Practicing in-race nutrition during long training runs can increase carbohydrate absorption capacity by 30–40%. Start by consuming calories on every run over 90 minutes, gradually increasing to race-level intake during peak training long runs. This prepares your GI system for race day demands.
Most runners can absorb 200–400 calories per hour during sustained exercise. The general recommendation is to replace 30–50% of calories burned. Lighter runners and slower paces favor the lower end; heavier runners at faster paces may need the higher end. Start conservatively and increase if your stomach tolerates it well.
Sodium is the primary electrolyte lost in sweat (700–1400 mg/liter). Over a 20+ hour race, you can lose 10,000–30,000+ mg of sodium. Hyponatremia (low blood sodium) from excessive water intake without adequate sodium can be life-threatening. Consistent sodium intake from the start prevents cramping, maintains fluid balance, and supports cognitive function.
There's no single best food — variety and personal tolerance matter most. Common choices: gels and energy chews (quick carbs), boiled potatoes with salt, PB&J sandwiches, pretzels, bananas, broth/soup (warmth + sodium), and candy (quick sugar). Many runners shift from sweet to savory foods after 6–10 hours. Test everything in training.
The gut has separate transport proteins for glucose (SGLT1) and fructose (GLUT5). Glucose absorption maxes out around 60 g/hr. Adding fructose uses a different pathway, allowing total carb absorption of 90+ g/hr with a 2:1 glucose-to-fructose ratio. Many commercial sports drinks and gels are now formulated with this ratio for maximum absorption.
General guidelines are 400–800 mL per hour, adjusted for conditions, sweat rate, and pace. In cool conditions, 400–500 mL may suffice. In hot conditions, 700–800+ mL may be needed. Weigh yourself before and after training runs to estimate your sweat rate. Aim to lose no more than 2–3% of body weight during the race.
Yes. In the first 4–6 hours, the gut typically tolerates higher calorie and carb intake (closer to 300–400 cal/hr). After 10–12 hours, GI function may decline and absorption decreases. Many runners shift to simpler foods (broth, plain carbs), reduce volume per serving, and increase frequency. In the final hours, solid food tolerance often drops and liquid calories (sports drink, cola, broth) become primary fuel.