Triathlon Race Nutrition Calculator
Calculate calorie and fluid needs for your triathlon by distance and intensity.
Get hourly carbohydrate intake targets and hydration amounts for each segment.
Proper race nutrition is the fourth discipline in triathlon. Getting it wrong leads to bonking (energy crash) or GI distress, both of which derail race performance.
Calorie burn rates by triathlon leg:
- Swimming: 600–800 kcal/hr
- Cycling: 500–900 kcal/hr (varies with power output)
- Running: 700–1,000 kcal/hr
Carbohydrate intake guidelines (g/hr):
- Races under 1 hour: No in-race fueling needed
- 1–2 hours: 30–60 g carbs/hr
- 2–3 hours: 60–90 g carbs/hr
- Over 3 hours: 60–90 g carbs/hr (with multiple carb sources)
Note: The human gut can absorb a maximum of ~60 g/hr of glucose alone, or up to ~90 g/hr when combining glucose + fructose sources. Over-fueling causes GI distress.
Hydration:
- General guideline: 500-750 mL per hour in moderate conditions
- Hot weather: 750-1,000 mL per hour
- Do not race on thirst alone. By the time you feel it, performance has already started to slip.
Those figures describe a 70 kg athlete, and the calculator scales them to the weight you enter. A 90 kg athlete sweats appreciably more than a 55 kg one at the same effort in the same weather, so the same number cannot be right for both. It is still only an estimate: the honest way to get your own figure is to weigh yourself before and after a hard hour and see what you lost.
Sodium: Replace roughly 500 mg per hour in cool conditions and up to 1,000 mg per hour in the heat, again scaled for body mass. Sports drinks, salt capsules and electrolyte tablets all get you there.
Why carbohydrate is the one target that ignores your weight. Fluid and sodium track sweat rate, which tracks body size. Carbohydrate does not, because the limit is not how much fuel you need. It is how fast the intestine can move sugar into the blood, and that transporter capacity is broadly the same across adults. This is why the guidance is an absolute grams-per-hour figure rather than grams per kilogram, and why a bigger athlete has to run a larger deficit rather than simply eating more.
Practical examples:
- Sprint (1 hr): minimal fuelling, a gel before the run is enough
- Olympic (2 hr): 1–2 gels on bike, 1 gel on run, 750 mL fluid
- Half Ironman (4–6 hr): 2–3 solid snacks + 4–6 gels, 3–4 L fluid total
- Ironman (8–17 hr): Full nutrition plan with real food, gels, and drinks
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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