Marathon Fueling Calculator
Plan your race-day carbohydrate intake: total grams, gels and per-hour targets from your expected finish time.
How it works
Total carbs = rate(g/h) × hours · gels = total ÷ carbs-per-gel · per-30-min = rate ÷ 2
Endurance guidelines suggest 30–60 g of carbohydrate per hour for efforts up to about 2.5 hours, rising toward 90 g/h for longer races when you combine glucose and fructose sources the gut can absorb through separate pathways. Spreading intake across regular small doses — for example every 20–30 minutes — keeps blood glucose steady and reduces stomach distress compared with a few large hits. This planner turns your target rate and finish time into a concrete gel count so nothing is left to guesswork on race morning.
Worked example
A 4-hour marathoner fueling at 60 g/h needs 60 × 4 = 240 g of carbohydrate. With 22 g gels that is 240 ÷ 22 ≈ 10.9, so 11 gels, or about 30 g (a gel and a bit) every half hour.
Frequently asked questions
How many carbs per hour should I aim for?
Most runners do well on 30–60 g/h. Rates of 70–90 g/h are achievable but require training the gut and using mixed glucose-plus-fructose products; do not try a new high rate for the first time on race day.
Do gels and sports drink count together?
Yes — add up carbohydrate from every source, including drinks, chews and real food. Enter your average carbs-per-serving to see the equivalent number of servings.
Should I practice my fueling plan?
Absolutely. Rehearse the exact products and timing on long training runs so your stomach is used to them and you have confirmed you can hit the target rate comfortably.
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Educational estimate only — not medical advice. Individual needs vary; consult a qualified professional before making health decisions.