Marathon Race Nutrition Calculator
Plan your marathon fueling strategy with exact carb, gel, fluid, and electrolyte targets.
Based on goal finish time and body weight for optimal race day performance.
Race Day Fuel Plan
Marathon Nutrition Strategy
The body stores roughly 1,800-2,000 calories of glycogen — enough for about 18-20 miles. To avoid “hitting the wall,” you must replace carbohydrates during the race.
Carbohydrate targets:
- Trained gut: up to 90g carbs/hour (glucose + fructose mix)
- Standard recommendation: 60g carbs/hour
- Conservative / new runner: 30-45g carbs/hour
Common gel sizes: 22-25g carbohydrates per gel
Fluid guidelines:
- ~16-24 oz (500-700 ml) per hour
- Hot weather: up to 24 oz/hour
- Cool weather: 12-16 oz/hour
Sodium (electrolytes):
- 300-600 mg sodium per hour
- Heavy sweaters may need 700-1,000 mg/hour
Timing: Start fueling at mile 4-6 (before you feel tired). Take a gel every 30-45 minutes. Never try anything new on race day — always test your nutrition plan during long training runs.