Triathlon Nutrition Calculator

A triathlon nutrition plan sets how much carbohydrate, fluid and sodium to take in during each hour of a race, and on which leg. Carbohydrate targets are set in grams per hour by how long the race lasts, not by body weight¹. Fluid is set from your own sweat rate, and nothing is taken in during the swim.

What a Triathlon Nutrition Plan Measures

It is a race-day plan built from expert guidelines, not a measure of what your body needs. It does not count calories or measure sweat. For carb loading in the days before and the race-morning meal, use the Carb Loading Calculator.

The Formula

Carbs for a leg (g) = carb target (g per hour) x leg time (hours)

Lowest fluid per hour = sweat rate x (1 - 2% of body weight / expected sweat loss)

Highest fluid per hour = sweat rate

Sodium for a leg (mg) = 300 to 600 mg per hour x leg time (hours)

Caffeine (mg) = 3 to 6 mg x body weight (kg)

The carb bands and 2 percent fluid limit come from the joint American College of Sports Medicine (ACSM) position², and the carb bands match a review written for the International Olympic Committee (IOC) nutrition consensus³.

How This Calculator Computes Your Result

Pick a race distance and enter your expected swim, bike, run and transition times. Your total time sets your carb band, and you pick a target inside it. You can also add body weight, your bike and run sweat rates (L/h or fl oz/h), the carbs on your gel and drink labels, salty sweat and caffeine. No sweat rate yet? Measure it with the Sweat Rate Calculator.

We use 1 lb = 0.45359237 kg and 1 US fl oz = 29.5735 mL, and round carbs to 5 g, fluid to 50 mL, sodium to 50 mg and caffeine to 5 mg. You get carbs for swim (always 0), bike and run, fluid and sodium ranges, and optional caffeine. Gel and drink amounts assume your lowest fluid amount is your sports drink, with gels making up the rest. For example, an Olympic race of 2 h 27 min at 45 g per hour gives 55 g on the bike and 35 g on the run. IRONMAN and 70.3 are trademarks of their owner, and this site is not affiliated with them.

What Your Result Means

Your carb band depends on your total race time² ³:

The body can use only about 60 g per hour of one type of sugar, such as glucose¹. Mixing glucose and fructose raised the rate of use by up to 75 percent, which is how higher intakes become usable¹. The International Society of Sports Nutrition (ISSN) gives 30 to 60 g per hour, as a 6 to 8 percent sports drink every 10 to 15 minutes⁴. These guidelines were written for well trained athletes, and slower or less trained athletes may need less¹.

The fluid range runs from the least you can drink and keep your loss within 2 percent of body weight, up to your sweat rate, with thirst as the guide inside that range. Losses above 2 percent can hurt performance, especially in the heat². Sodium is shown as 300 to 600 mg per hour, a guideline for prolonged exercise⁵. It matters most if you sweat more than 1.2 L per hour, have salty sweat, or race for over 2 hours².

Caffeine is shown as 3 to 6 mg per kg, usually taken about 60 minutes before the start⁶ ⁷. A lower dose under 3 mg per kg (about 200 mg), split before and during exercise with carbohydrate, is another option, and 9 mg per kg or more adds side effects without extra benefit⁷. The FDA cites 400 mg a day as an amount not generally linked to negative effects for most adults⁸.

Why the Bike Leg Carries Most of the Fueling

You cannot eat or drink in the swim, so fueling starts on the bike. The bike is the longest leg and the easiest place to eat, so it carries the biggest share of your carbs. In a study of Ironman athletes, most of the intake happened during the cycling leg¹. In two Ironman races, athletes averaged 62 and 71 g per hour, and higher intake was linked to faster finishes but also to more nausea⁹. About 31 percent of Ironman athletes had serious gut symptoms⁹.

Gut Training and the 90 to 120 g per Hour Option

The gut adapts to what you feed it. In one study, 28 days of a high carbohydrate diet raised how much carbohydrate athletes could use from drinks during exercise, and practicing high intakes made the stomach more comfortable¹⁰. Stomach problems affect 30 to 50 percent of athletes, so race intake is best practiced in long sessions¹⁰.

Newer studies test 120 g per hour. In 11 highly trained cyclists, 120 g per hour raised the use of ingested carbohydrate by about 17 percent compared with 90 g, but it did not spare the body's own stores, and performance was not tested¹¹. In 20 elite, gut-trained mountain runners, 120 g per hour lowered markers of muscle damage, but race times did not differ¹². A 2022 review concluded the 90 g per hour maximum cannot yet be changed¹³, so 90 to 120 g per hour is an opt-in option for trained guts only.

Fluid, Sodium and the Risk of Overdrinking

Exercise-associated hyponatremia means low blood sodium, usually below 135 mmol/L, and its main cause is drinking more than you lose¹⁴. In Ironman races, low blood sodium without symptoms was found in up to 18 percent of athletes in one study and 25 percent in another¹⁴. Risk is higher in events over 4 hours, at a slow pace, and in athletes who gain weight during the race¹⁴. The consensus advice is to drink when thirsty, and sodium cannot prevent it if you keep overdrinking⁵ ¹⁴. That is why this calculator never shows fluid above your sweat rate.