Carbs per hour, by duration and intensity

Educational content, not medical advice. Individual tolerance varies; persistent GI symptoms or any race-related medical concern should be reviewed by a sports dietitian or doctor.

Ask ten endurance athletes "how many carbs per hour should I take?" and nine of them will say 60 grams. That number is everywhere, on every blog, in every coach's quick answer. It's also wrong about half the time. 60 g/h is the midpoint of a range, not a target. The right number depends on how long you'll be racing, how hard you'll push, what your gut has been trained for, and what fuel form you're using. This guide turns the midpoint back into a band you can actually plan around.

If you want the number tailored to your race instead of working through the band manually, our race-day fueling planner at planner.nutrifinder.it does the maths from your weight, sport, distance, and target time. It's free and no signup is needed for the first plan. The rest of this guide is the why behind the number it shows you.

The number you've been quoted is too neat

The Burke et al. consensus and the ACSM position stand both publish carb intake bands, not point values. The most commonly cited table looks like this:

Event duration	Carb intake target	Fuel type that works
Under 1 hour	0 g/h (mouth rinse optional)	Water alone is fine
1 to 2 hours	30 g/h	Glucose or maltodextrin only
2 to 3 hours	60 g/h	Glucose or maltodextrin only
Beyond 2.5 hours	60 to 90 g/h	Multi-transportable (glucose + fructose)
Ultra-endurance, elite	90 to 120 g/h	2:1 or 1:0.8 glucose-fructose, gut-trained

Two things to read out of this. First, for events under an hour, you don't need to eat anything. Your glycogen stores cover it. A carb mouth rinse can sharpen the back end of a 5K or 10K, but ingesting calories at that pace mostly means you're swallowing fluid you didn't need and risking GI symptoms for no metabolic return. Second, the jump from 60 g/h to 90 g/h is a fuel-form change, not just a quantity change. Past 60 g/h, you have to use a product that contains fructose or you'll saturate the SGLT1 transporter (see the gut-training guide for the physiology).

Duration is the lead variable, not intensity

This is the part most athletes get backwards. They reason "I'm racing harder, so I need more fuel." The maths actually runs the other way. Carb oxidation rate is what you can absorb and burn, and it scales with time at sustained effort, not with how spicy that effort feels. The 60-90 g/h band assumes a steady aerobic intensity around tempo or just below threshold. Push above threshold for sustained periods and blood is shunted away from the gut, gut absorption drops, and your effective intake ceiling falls, not rises.

A practical way to think about this:

• Short and hard (under 90 minutes at high intensity): your problem is glycogen depletion, not refueling rate. Top up with a small dose pre-start and you're done.
• Long and steady (over 2 hours at tempo): your problem is sustained refueling. Hit 60 g/h minimum, push toward 90 g/h if your gut handles it.
• Long and hard (over 4 hours with sustained surges): both. You need the high-end fueling rate and a strategy to take it in during the steady stretches, not the climbs.

Heat amplifies the same effect. Above roughly 28°C, gastric emptying slows; your trained 90 g/h tolerance might land at 70 g/h on a hot day. Plan the floor of the band, not the ceiling, when the forecast goes red.

The first-hour rule: ramp in, don't front-load

The single most common pacing mistake is the front-load. "I feel great in the first hour, let me bank some carbs while I can." It backfires for two reasons. First, in the opening 30-45 minutes your body is still settling into the effort; nutrient flow is not yet optimal and a big bolus tends to sit. Second, carbs you take early don't bank, they oxidize at the same per-hour ceiling as carbs you take later. There is no front-loading.

The race-day pattern that works:

1. Minutes 0-30: nothing, or sips of water. The gun-to-first-fuel window is part of the warm-up.
2. Minute 30: first intake at the bottom of your target band. Settle the gut into "we're working now."
3. Minutes 30 to final 30: steady 25-30 minute intervals, hitting your target rate.
4. Final 30 minutes: stop intake. Carbs taken inside this window don't reach your muscles in time.

Two practical implications. If your race is 90 minutes, you have one meaningful intake window (around minute 30) and that's it. Stick to 30 g/h, take one gel, and stop thinking about it. If your race is 4+ hours, you have 6-7 intake windows and the back half is where races are won or lost; the athletes who fade are almost always the ones who tapered off intake at hour 3 because they were suffering.

Caffeine: a multiplier, not a substitute

Caffeine is the most studied legal ergogenic aid for endurance sport. It works, the effect size is real (~2-4% performance improvement), and it stacks on top of carb intake rather than replacing it. The mechanism is two-fold: caffeine reduces perceived effort and it increases fat oxidation, which spares glycogen. Together with carbs, it lets you hold a higher effort for longer.

Practical dosing:

• 3-6 mg per kg of body weight, total dose, across the race. For a 70 kg athlete that's 210-420 mg.
• Peak effect is 45-60 minutes after ingestion. Time it for when you need it, not for "now."
• Don't stack with new carb products on race day. Caffeine can irritate the gut on its own. If you're trying both for the first time, you'll never know which one caused the problem.
• Withdraw or maintain, don't yo-yo. Some athletes "de-caffeinate" for the week pre-race; this can sharpen the response but only if you actually went without for 5-7 full days.

A simple race-day caffeine plan: one 50 mg dose 30-45 minutes pre-start, a 100 mg dose at the halfway point of a long race, and a 100 mg caffeinated gel 45-60 minutes before the planned final push. That's 250 mg total for a 70 kg athlete - well inside the band and timed to peak at the moments that matter.

Worked examples by race distance

These are starting points for a gut-trained athlete in temperate conditions. Adjust the floor by 10-15 g/h for heat, for new product, or for an untrained gut.

10K (35-50 minutes): no in-race fueling needed. Optional: half a gel 15 minutes pre-start to settle nerves. Caffeine 30-45 minutes pre-start at the high end of your tolerance.

Half-marathon (75-110 minutes): 30 g/h. One gel at minute 30, optional second at minute 60 if you're slower than 1:45. Glucose or maltodextrin only is fine; no need for multi-transportable products at this duration.

Marathon (2:30-4:30): 60 g/h, possibly 75 g/h for slower finishers. Two to three gels per hour or equivalent in sports drink. This is the threshold where a glucose-fructose mix starts to matter, especially for athletes finishing over 3:30.

70.3 / Half Ironman (4-6 hours): 75-90 g/h. Mostly liquid carbs on the bike for absorption, gels on the run when you can't carry bottles. Caffeine timed for the last 60-90 minutes of the run.

Full Ironman (9-15 hours): 70-90 g/h on the bike, 60-75 g/h on the run. Total carb intake over the day commonly lands at 700-1000+ grams. This is where gut training is non-negotiable; nobody finishes well at full Ironman intake without it.

What to do if you're new to the band

Start at the floor of the duration band, train at it for two long sessions, then push the rate up by 10-15 g/h every two weeks until you find your ceiling. The gut-training guide has the full protocol. The planner will scale its recommendation as your gut tolerance climbs; the band is a target, not a verdict.

Get a plan for your race

The bands above are the general rules. To turn them into a per-30-minute plan with specific products, fluid volumes, and caffeine timing for your race, open the NutriFinder planner. Enter your weight, the sport, the distance, and the conditions; it returns the carb target, the sodium target, the fluid target, and a timeline you can take to the start line. The planner runs on the exact bands and reference values cited in this guide, no black box.

Research and references

The numbers and protocols in this guide rest on the following peer-reviewed sources. Verify the dose, the side-effect profile, and the contraindications against the primary literature, not against any single source.

1. Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. 2011. Journal of Sports Sciences. Carbohydrates for training and competition. PMID 21660838
2. Thomas DT, Erdman KA, Burke LM. 2016. Medicine & Science in Sports & Exercise. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. PMID 26891166
3. Jeukendrup AE. 2014. Sports Medicine. A step towards personalized sports nutrition: carbohydrate intake during exercise. PMID 24791914
4. Spriet LL. 2014. Sports Medicine. Exercise and sport performance with low doses of caffeine. PMID 25355191