How it works
carbs/hour by duration: <1 h ≈ 0 · 1–2 h ≈ 30 g · ≥2 h ≈ 60 g (up to 90)
Stored glycogen covers roughly the first 90 minutes of hard running, and the banding follows from that: finishes under an hour get a 0 g/h target because pre-race eating carries you through, one-to-two-hour efforts get 30 g/h, and anything beyond two hours gets 60 g/h — with up to 90 g/h available to runners who have trained their gut on glucose-plus-fructose products. Total grams equal the hourly rate times your hours on course; the gel count divides that total by 25 g and rounds up. Sodium is planned at a flat 500 mg per hour, a midpoint of the 300–800 mg/h span that covers most sweat profiles — heavy or salty sweaters should verify with a sweat test instead of trusting the midpoint.
Sources
- Carbohydrate during exercise Jeukendrup, A. (2014). “A step towards personalized sports nutrition: carbohydrate intake during exercise.” Sports Medicine 44(S1), 25–33 — 30–60 g/h, up to ~90 g/h with multiple transportable carbohydrates for long events.
- ACSM/ISSN guidance American College of Sports Medicine / International Society of Sports Nutrition — carbohydrate intake scales with exercise duration; ~30–90 g/h for events over ~1–2.5 h.
- Sodium replacement Sweat sodium losses commonly fall around 300–800 mg per hour; replacement needs are individual and rise with heat and sweat rate.
FAQ
How many gels should I carry for a marathon?
Let the total-carbs figure do the division: a 3:30:00 finisher at 60 g per hour needs about 210 g, which rounds up to nine 25 g gels. Carry one beyond the computed count — a dropped gel or a missed aid station should not be able to unravel the plan.
Why does the calculator only ask for my finish time?
Because duration is what drains the tank. Carbohydrate need scales with how long you run far more than with how far, so the tool bands its hourly target by expected hours on course. Unsure of your time? Estimate generously — fueling for 4:15 and finishing in 4:00 beats the reverse.
Do I need in-race fuel for a 5K or 10K?
No — under an hour the plan comes back as 0 g/h on purpose, since normal meals stock more glycogen than those distances burn. Put the attention into hydration and into eating well in the day or two beforehand instead.
When should the carbs actually go in?
Evenly, from early on — first gel around 30–45 minutes in, then at regular intervals — rather than back-loaded once you feel flat. Absorption takes time, so a gel swallowed at the moment the bonk arrives shows up in your bloodstream about twenty minutes too late.
Can I push past 60 grams per hour?
A trained gut can reach about 90 g/h, but only with products mixing glucose and fructose, which use separate absorption routes across the intestinal wall. Build toward it over weeks of long runs; jumping straight to 90 g/h on race morning is a reliable recipe for GI trouble.
How trustworthy is the 500 mg/h sodium figure?
It is a deliberate midpoint, not a measurement of you. Hourly sweat sodium losses commonly span 300–800 mg and swing with heat, fitness, and genetics — some runners sit outside the band entirely. Lean higher in hot races or if you finish workouts crusted in salt, and confirm with a sweat test.
These targets are duration-banded starting points drawn from published sports-nutrition guidance, not a personalized plan — carbohydrate tolerance and sodium loss differ enormously between runners. Rehearse every product and dose in training before racing on it, and involve a sports dietitian or physician if you have GI, kidney, or blood-pressure concerns. Informational only, not medical advice.