Free race-day nutrition tool
Marathon fuel calculator
Build a marathon fueling plan that turns your pace, gel choice, body metrics, sweat profile, and weather into clear gel timing, carb targets, hydration, sodium, caffeine, and pre-race carb guidance.
Distance
42.2 km
Uses full marathon distance by default.
Carb target
60-90 g/h
Adjustable based on pace, body size, and gut tolerance.
First fuel
20-30 min
Start before energy drops, then repeat by target cadence.
Build your race fuel plan
Calculate a marathon fueling plan from your target pace, gel product, carb target, body metrics, weather, and sweat profile. Connect a mapped race course if you want the plan aligned to real aid stations.
How to use this calculator
Start with the race distance, then personalize the plan around the fuel you actually use in training.
Choose marathon as the race type, or connect a supported marathon course.
Enter target pace, gel carbs, body metrics, heat, sweat rate, and sweat saltiness.
Generate the plan to see gel timing, total carbs, hydration, sodium, caffeine, and pre-race carb targets.
Fuel calculator FAQ
Quick answers for race-day carbs, gel timing, hydration, and distance-specific fueling decisions.
How many gels do I need for a marathon?
Most marathon runners need about 5 to 10 gels, depending on finish time, grams of carbs per gel, and target carbs per hour. The calculator uses your target pace and product choice to calculate the exact count.
What should my marathon carbs per hour target be?
Many marathon plans land around 60 to 90 grams of carbs per hour. Faster, well-trained, or larger runners may target the higher end, while runners with GI sensitivity may start lower and train up.
When should I take my first marathon gel?
A practical marathon starting point is 20 to 30 minutes after the start. Taking fuel early helps maintain glycogen availability instead of waiting until fatigue is already building.