Carbohydrate Fueling Calculator
Carbs per hour and total — plus how many gels to carry.
Why carbohydrate fueling matters
Your muscles and brain run on a limited store of glycogen. In efforts beyond about an hour, taking in carbohydrate during the event keeps blood glucose up, spares that store, and delays the fade that comes from running low — which is why fueling is one of the biggest levers in long-distance racing.
How much per hour
Under an hour you usually need little or none. For 1–2.5 hour efforts, roughly 30–60 g/hr is enough; beyond 2.5 hours the target rises to 60–90 g/hr, and well-trained athletes racing hard and long now push toward 90–120 g/hr. Harder intensity and longer duration both raise the number.
Going above 60 g/hr
Glucose is absorbed through the SGLT1 transporter, which saturates near 60 g/hr. Adding fructose opens a second pathway (GLUT5), letting a trained gut take in 90 g/hr or more, typically in roughly a 1:0.8 glucose-to-fructose ratio. Practise high rates in training so your gut adapts before race day.
Questions
How many carbs per hour do I need?
Under an hour, you usually need little or none. For 1–2 hour efforts, 30–60 g/hr works; beyond 2 hours, 60–90 g/hr; and trained athletes targeting hard, long races now push 90–120 g/hr using glucose-plus-fructose mixes.
Why does going above 60 g/hr need fructose?
Glucose is absorbed through the SGLT1 transporter, which saturates around 60 g/hr. Adding fructose (absorbed via GLUT5) opens a second pathway, letting well-trained guts take in 90 g/hr or more — usually in a roughly 1:0.8 glucose-to-fructose ratio.
Should I train my gut?
Yes. High intake rates can cause stomach distress if you have not practised them. Rehearse your race-day carb rate in long training sessions so your gut adapts before race day.