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Marathon fueling planner

Turn a carbs-per-hour target into a simple fueling schedule you can practice in training and execute on race day.

Last updated/Feb 03, 2026, 02:17 PM

Tool

Inputs → outputs

This page is intentionally practical: get numbers first, then read the how-to.

Inputs

  • Finish time (hh:mm)
  • Carbs per hour (g/h)
  • Dose interval (minutes)
  • Carbs per gel (g) (optional)

Outputs

  • Total carbs (g)
  • Approx gels (count)
  • Dose schedule

Examples

3:45 marathon @ 75g/h
Total ≈ 281g carbs (≈ 12 gels @ 25g) with a 20-minute schedule.
4:20 marathon @ 60g/h
Total ≈ 260g carbs (≈ 11 gels @ 25g) with a 25-minute schedule.

Planner

Marathon fueling schedule

A simple, repeatable plan: pick a carb target, then schedule doses you can actually execute while running.

Total time

3:45:00

Total carbs

281 g

Approx gels

12 gels

Simple schedule

Take a dose every 20 minutes. In training, practice the same timing so race day is automatic.

20m40m60m80m100m120m140m160m180m200m220m

Safety note: fueling targets vary by athlete and conditions. Practice in training and adjust if you get GI distress. This is not medical advice.

Assumptions

What this tool assumes

  • Carb target is a training-tested number for you (GI tolerance varies).
  • You can execute the schedule while running (practice with the same products).

Limitations

What can break it

  • Does not prescribe medical nutrition or account for diabetes or GI disease.
  • Heat, intensity, and aid-station options change what’s practical; adjust on race week.

Related

Use this with a plan

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FAQs

What carb target should I use?

Use a target you can tolerate in training. Many athletes land somewhere between 60–90 g/h, but the right number is individual.

When should I start taking carbs?

Earlier than you think. A simple rule is start within the first 30 minutes, then follow the schedule.

Do I need sodium?

It depends on sweat rate, heat, and what you tolerate. If you use electrolytes, practice with them in training and avoid overdoing it.

Keep going

Sources