Half marathon fuel calculator

Create a half marathon fueling plan that estimates how many gels you need, when to take them, how much water to pair with fuel, and whether your target pace needs light or full race-day fueling.

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 72 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.

Half marathon

21.1 km

1:56:02

Finish time at 5:30 per km

Carbs per hour
75 g
Gels
5
Fluid per hour
600 to 900 ml

Free. No account needed.

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

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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 half 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 half marathon as the race type, or connect a supported half 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

  • Runners finishing under 75-90 minutes may need less fuel than runners racing for two hours or more.
  • The calculator lets you adjust carbs per hour instead of forcing a one-size-fits-all gel count.
  • Course-connected plans align fuel timing with known aid stations when mapped course data exists.

Fuel calculator FAQ

Quick answers for race-day carbs, gel timing, hydration, and distance-specific fueling decisions.

Do I need gels for a half marathon?

If your half marathon will take longer than about 60 minutes, taking carbs during the race can help maintain pace. Faster runners may only need one or two gels, while two-hour runners often benefit from more.

How many gels should I take in a half marathon?

Most runners use 1 to 4 gels in a half marathon. The right number depends on finish time, gel size, target carbs per hour, and how well you tolerate fuel at race pace.

When should I take my first half marathon gel?

A common starting point is 20 to 30 minutes into the race. If you expect to finish quickly, one early gel may be enough; longer finish times usually need a repeat intake later.

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