Ultra Marathon Nutrition Calculator

About the Ultra Marathon Nutrition Calculator

The Ultra Marathon Nutrition Calculator estimates your calorie, carbohydrate, sodium, and fluid requirements for ultra-distance races. Fueling is one of the bigger challenges in ultra running, because small mistakes can compound over many hours.

This calculator accounts for your body weight, target pace, race distance, and environmental conditions to generate a 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 structured nutrition plan can improve your odds of finishing well. Practice every element of your plan in training — race day is not the time to experiment.

When This Page Helps

Ultrarunning nutrition is more complex than shorter-distance racing because calorie absorption, sodium loss, and hydration tolerance all shift over time. It shows planning targets that can serve as the foundation of a race nutrition plan, then you can refine them based on training runs and personal tolerance.

How to Use the Inputs

1. Enter your body weight in pounds or kilograms.
2. Select the race distance (50K, 50 Mile, 100K, 100 Mile, or custom).
3. Enter your estimated average pace (min/mile or min/km).
4. Select conditions: cool, moderate, or hot/humid.
5. View hourly targets for calories, carbohydrates, sodium, and fluid.
6. Use the timeline table to plan aid station intake.

Example Calculation

Tips & Best Practices

• Practice your race nutrition plan during long training runs. Your gut adapts to taking in calories while running - train it gradually.
• Mix glucose and fructose sources (2:1 ratio) to maximize carb absorption beyond the ~60 g/hr single-source limit.
• Have a variety of food options: gels, chews, real food (potatoes, PB&J, broth). Taste preferences change during ultras.
• Take sodium consistently from the start, do not wait until you cramp. By the time you cramp, you are already behind.
• In hot conditions, adjust sodium and fluid upward relative to moderate conditions, but keep the plan within what your stomach can tolerate.
• Reduce calorie-intake ambitions in the final 2-3 hours - GI tolerance often worsens late in the race.
• Use a simple spreadsheet or chart marking what to eat/drink at each aid station.

Building Your Race Nutrition Plan

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.

Common Nutrition Mistakes

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 is hard 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.

Adaptation and Training

The gut is highly trainable. Practicing in-race nutrition during long training runs can improve carbohydrate tolerance over time. 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.

Frequently Asked Questions

• How many calories should I eat per hour during an ultra?

  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.

• Why is sodium so important in ultras?

  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 helps prevent problems and supports fluid balance.

• What foods work best during an ultra?

  There is 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.

• What is the glucose-fructose transport system?

  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 higher absorption.

• How much should I drink per hour?

  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.

• Should my nutrition plan change as the race goes on?

  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, liquid calories often become the easiest fuel source.