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.

Race
Distance
Optional

Without a course, fuel is timed by the clock.

Minutes and seconds, like 5:30.

Fuel

Leave empty to use the recommended 92 g for your finish time.

Water during the race
About you
Sex
Weather and sweat
Race-day weather
Sweat rate
Salt in your sweat

Salty if your kit shows white marks after long runs.

Marathon

42.2 km

3:52:04

Finish time at 5:30 per km

Carbs per hour
100 g
Gels
14
Fluid per hour
600 to 900 ml

Free. No account needed.

Drink to thirst. Fluid is a range, not a target.

Missing your race, or something looks wrong? Email us

Want training-aware nutrition around this race? See Mavr on the App Store

General guidance for healthy adults, not medical advice. Talk to a doctor or registered dietitian if you have a health condition, take medicines or have special dietary needs. Caffeine advice is for healthy adults only. EFSA's safe limit is 200 mg in one dose and 400 mg in a day.

How to use this calculator

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.

Start with the race distance, then personalize the plan around the fuel you actually use in training.

  1. 1Choose marathon as the race type, or connect a supported marathon course.
  2. 2Enter target pace, gel carbs, body metrics, heat, sweat rate, and sweat saltiness.
  3. 3Generate the plan to see gel timing, total carbs, hydration, sodium, caffeine, and pre-race carb targets.

How the plan is built

  • The calculator builds a time-based plan when no course is selected.
  • Course-connected plans align fuel and water to mapped aid stations when course data is available.
  • You can override carbs per hour if your gut training or coach gives you a specific target.

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.

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