FORGE

Race fueling calculator.

Grams of carbohydrate, millilitres of fluid and milligrams of sodium per hour, from how long you'll be out and how hard you'll go — with the totals to pack.

hours

Your expected finish time, or the length of the session.

Effort
Carbs per hour
75–90g
Fluid per hour
400–800ml
Sodium per hour
300–1000mg

For 5 hours, 2.5 hours and up: 60–90 g/h from a glucose:fructose blend.

Carbs for the day
375–450g
In gels (~25 g)
15–18
Fluid for the day
2–4L
  • Start in the first 20 minutes and keep a steady drip — a gel every 20–30 minutes beats three in the last hour.
  • Above 60 g/h, use a glucose:fructose mix (most race gels and drink mixes are): two sugars use two doors into the blood.
  • With a trained gut you can take 90–120 g/h. Train it: practise race intake on every long session from your build phase on.
  • Nothing new on race day: every product and amount here should be one you've used in training.

How to use it.

Carbohydrate is the limiter on anything over about 90 minutes: you store enough for roughly two hours of hard work, and the rest has to come in through your mouth while you move. The target scales with duration. Under an hour you need nothing. Between one and two hours, 30 to 60 grams an hour of any sugar you tolerate. Beyond two to two and a half hours, 60 to 90 grams an hour — and at those rates the mix matters, because the gut absorbs glucose and fructose through separate doors, so a 2:1 or 1:0.8 glucose-to-fructose blend gets more in than glucose alone.

Train your gut like your legs. Intake rates in the 90 to 120 g/h range that elite marathoners and Tour riders now use are possible for most athletes only after weeks of practice: the gut adapts to carry more. Take your race intake on every long session from your build phase onward, with the same products, in the same amounts, at the same times. If something goes wrong in training, that is cheap information; on race day it is the race.

Fluid and sodium are individual, so the calculator gives ranges. Most athletes do well between 400 and 800 ml an hour, more in heat, and sodium somewhere between 300 and 1,000 mg an hour. Weigh yourself before and after a long session: each kilogram lost is about a litre of sweat, and a loss over 2 to 3% of body weight is where performance drops. Drink to that number rather than to a schedule or to thirst alone, and put most of the sodium in the drink, not in pills taken dry.

Questions.

Is 90 g/h too much for me?

Only if you haven't trained for it. Start at 60 g/h, practise on every long session, and add 10 g/h every two to three weeks while your stomach stays settled. Many age-groupers race comfortably at 80–90 g/h after a block of practice.

Gels, drink or real food?

All three work; the carbohydrate doesn't care about the wrapper. Drink mix is easiest to dose steadily, gels are easy to carry, and solid food suits the bike leg of a long race better than the run. Count the grams, not the number of items.

What about the carb load before the race?

For races over about 90 minutes, 8–12 g of carbohydrate per kilogram of body weight per day for the final 36–48 hours, from low-fibre, familiar foods. Expect to gain a kilogram or two — that is stored fuel and the water that comes with it, not fat.

Where do these numbers come from?

Asker Jeukendrup's duration-based carbohydrate guidance, the ACSM position stand on nutrition and athletic performance, and 220 Triathlon's Ironman fueling guide. They are listed below. A FORGE plan sets your daily targets from the same work.

Sources

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