Half Marathon Race Day Nutrition Carbs, Caffeine, and Your Fuelling Plan

Every source gives you the same 30-60g-per-hour carb range for race day, and you're left guessing where in that range your own number actually sits. Aim for 30-60g of carbs per hour if you'll be racing longer than 75-90 minutes, starting after the first 45-60 minutes. As a personalised starting point, target roughly 0.7-1.0g of carbs per kg of bodyweight per hour, then fine-tune from training-run testing. Below: how to personalise that number, caffeine dosing, fuelling for slower finishers, what to do when the course's gels don't match yours, and GI-safe options if your gut has let you down before.

Get this wrong and you don't just run slower — you're the runner queuing for a portable toilet at mile 8, or hitting a wall at mile 10 that felt completely avoidable in hindsight. Almost none of that is bad luck. It's an untested gel, a guessed carb number, or a dose you'd never tried before race morning.

Personalising Your Carb and Fluid Targets

Every ranking page gives you a population range and then defers to "consult a dietitian." That's not useful two weeks before your race. Here's the self-serve method I actually use with athletes.

Start with the carb formula: 0.7-1.0g of carbs per kg of bodyweight per hour. A 65kg runner lands at 45-65g per hour — the upper-middle of the standard range, based on body size, not guesswork.

Then run the sweat-rate test: weigh yourself nude before and after a 60-minute run with a known fluid intake logged. Each kilogram of bodyweight lost equals roughly 1L of sweat deficit. Use that result to target 400-800ml of fluid replacement per hour, adjusted upward in race-day heat. This is the exact tool I have athletes run through 2-3 weeks before race day, not a generic calculator handed to everyone.

Race-Day Caffeine Strategy

Every source says caffeine is "fine if you're used to it," with no concrete number attached. Here's the number: 3-6mg of caffeine per kg of bodyweight, taken 45-60 minutes pre-race as a single dose.

For finish times over 90 minutes, split it — half pre-race, half via a caffeinated gel at the 45-60 minute mark. A 65kg runner's total dose works out to 195-390mg, roughly 2-4 cups of coffee, or three to five caffeinated gels at around 75mg each.

One explicit rule: never trial a new dose or delivery method on race morning — test it in a training run first. An athlete I coached tried a double-strength caffeinated gel for the first time on race morning and needed an unplanned bathroom stop at mile 6. Test it before race day, always.

Fuelling for Slower Finishers (3+ Hours)

Most fuelling advice is calibrated to a 1.5-2.5 hour finish window, and it doesn't scale cleanly to a longer race. Total carb need scales with time on course, not just your hourly rate — a 3.5-hour finisher benefits from a wider variety of fuel sources across more feeding windows.

Real food, in addition to gels, becomes more viable and is often better tolerated over a longer race. Fluid intake shifts too: smaller, more frequent volumes — 150-250ml every 20 minutes rather than larger amounts every hour — to avoid GI overload across the longer duration.

When the Course's Gels or Drinks Don't Match What You Trained With

This is a common logistics gap that almost nobody covers. Check the race's official on-course product 2-3 weeks out, and train with that exact brand at least twice before race day where possible.

If a mismatch turns up late, carry your own full race supply rather than risk an untested product mid-race. If you're forced to use an unfamiliar on-course product anyway, take it in smaller or diluted increments than instructed, and pair it with extra water to reduce GI risk.

Nutrition for GI Sensitivity or IBS

"See a dietitian" isn't an answer if you're two weeks from race day with a gut that's let you down before. Here's a concrete tailored approach I build and rehearse with athletes rather than a generic referral out.

Favour low-FODMAP, glucose-only gel formulas over fructose-heavy blends, a common trigger for GI-sensitive runners. Reduce fibre and fat intake in the 24 hours before the race. And build and rehearse a fallback minimal-intake race plan — water and electrolytes only, no solid carbs — in training, for the runners whose gut doesn't tolerate on-course fuel at all.

Race Morning and the Night Before

The night before: a familiar, moderate-carb dinner, avoiding new foods, excess fibre, and alcohol. Race morning: 2-3 hours pre-race, 1-4g of carbs per kg of bodyweight, low-fat and low-fibre, familiar foods like toast and banana or oats. Stop solid food 60-90 minutes before the start.

Frequently Asked Questions

Do I need to eat during the race if I'll finish under 90 minutes?

Not necessarily. Under 75-90 minutes, your glycogen stores can usually cover the effort without extra carbs. Above that window, aim for 30-60g of carbs per hour starting after the first 45-60 minutes.

What should I eat for breakfast race morning?

Familiar, low-fat, low-fibre food 2-3 hours before the start — think toast and banana, or oats. Target 1-4g of carbs per kg of bodyweight, and stop solid food 60-90 minutes before the gun.

How many grams of carbs per hour during the race?

30-60g per hour for races longer than 75-90 minutes. As a personalised starting point, target roughly 0.7-1.0g of carbs per kg of bodyweight per hour, then fine-tune from training-run testing.

Is it okay to drink coffee before my half marathon?

Yes, if you're used to it — 3-6mg of caffeine per kg of bodyweight, taken 45-60 minutes pre-race, works well for most runners. Never trial a new dose or delivery method on race morning; test it in training first.

What should I eat the night before?

A familiar, moderate-carb dinner, avoiding new foods, excess fibre, and alcohol. This isn't the night to experiment with a restaurant you've never tried.

What should I do if I get stomach problems mid-race?

Switch immediately to water and electrolytes only, and drop solid carb intake until symptoms settle. Runners with a history of GI sensitivity should rehearse this minimal-intake fallback in training, not discover it for the first time on race day.

Can I use real food instead of gels?

Yes, especially for slower finishers running 3+ hours, where real food is often better tolerated than gel after gel. Test whatever you choose in training first, same as any other fuelling method.

What should I eat immediately after finishing?

A combination of carbs and protein within the first 30-60 minutes starts recovery efficiently. It doesn't need to be complicated — a recovery drink, or simply a proper meal if one is close by, both work.

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