Free tool
Triathlon race fueling calculator
Carbs per hour, fluid, and sodium for every leg of a sprint, Olympic, 70.3, or full-distance Ironman — built from your goal finish time, your body weight, and the fueling rate you have actually practised. Nothing here prescribes a rate you have never trained, because a race-day nutrition plan you cannot stomach is worse than no plan at all. Same engine that runs inside the Fuelog app.
| Leg | Time | Carbs | Total | Fluid | Sodium |
|---|---|---|---|---|---|
| Swim | 0h 36m | — | — | — | — |
| Bike | 3h 12m | 63 g/h | 200 g | 2 L / 68 oz | 2003 mg |
| Run | 2h 12m | 45 g/h | 100 g | 1.4 L / 47 oz | 1399 mg |
- Capped at your trained 60 g/h rather than the 105 g/h this duration supports. Gut training closes that gap.
- Your bike rate is above 60 g/h, so you need mixed glucose:fructose (1:0.8). A single-source product will not absorb fast enough and will sit in your gut.
- Using the 0.9 L/h population default. Do a sweat-rate test — individual rates vary more than any other variable here.
- Practise this exact plan on at least two long sessions before race day.
Your gut is the limit, not the guideline
105 g/h needs roughly 13 weeks and you have 10. Race at 100 g/h — a rate you have actually trained beats one you have only read about.
Carb loading
11.5 g/kg — about 861 g of carbohydrate a day for the 36–48 h before the start.
Caffeine
225–449 mg across the race (3–6 mg/kg). Only if you already use it in training.
Use a mixed-carb product
Above 60 g/h you need glucose:fructose at 1:0.8. Glucose transport saturates around that rate, and fructose crosses on a separate transporter — a single-source drink or gel physically cannot absorb fast enough.
This is one race. Fuelog is the whole build.
The same engine runs inside the app, where it uses your real training load from Whoop, Garmin or Apple Watch — periodizing carbohydrate from base through taper, tracking energy availability, and moving this plan every time your trained tolerance goes up.
Educational tool, not medical or dietary advice. Every number here is a starting point to practise in training — never try a new fueling plan for the first time on race day. If you have a medical condition affecting nutrition or hydration, talk to a qualified professional.
How race fueling actually works
Why carbs per hour scales with race duration
You start a race with roughly 400–500 g of stored glycogen — about 90 minutes of hard work. A sprint triathlon finished in 75 minutes runs almost entirely on what is already on board, so 30–60 g/h is plenty and under an hour you may need nothing but a mouth rinse. Past two hours, stored fuel becomes the limiter rather than fitness: Olympic distance sits in a 60–90 g/h band, and anything over three hours — every 70.3 and every Ironman — belongs in the 90–120 g/h band that long-course racing has moved to over the last decade.
Those upper numbers are only possible because of transporter physiology. Glucose crosses the gut wall on SGLT1, which saturates near 60 g/h. Fructose uses GLUT5, an entirely separate route, so a glucose:fructose blend around 1:0.8 lets you absorb well past the single-sugar ceiling. Above 60 g/h a single-source drink or gel physically cannot keep up — it sits in your stomach and becomes the GI distress people wrongly blame on “too many carbs.”
Why the bike gets more than the run
Same athlete, same day, different gut. On the bike you are stable, your hands are free, bottles and food are within reach, and there is very little mechanical jostling of the stomach. On the run, gastric emptying slows, blood is shunted away from the gut to working muscle, and every footstrike shakes whatever is in there. So this calculator runs the bike slightly above your target rate, drops the run about 25% below it, and prescribes nothing for the swim, where there is nothing practical to take anyway. The bike is where you bank the race’s calories; the run is where you spend them. Front-load accordingly — an Ironman marathon is not the place to discover you are 300 g behind.
Why the trained-tolerance cap matters more than the guideline
Absorption capacity is trainable, and it is the one number here you cannot fake. Handing 110 g/h to an athlete whose longest ride has been fuelled at 60 is how you write a DNF at mile 60 of the bike. That is why this plan never prescribes above the rate you enter — it caps, and then tells you how long the ramp would take. Roughly +10 g/h every two to three weeks of deliberate practice on your long session is the realistic rate of gain, so going from 60 to 110 g/h is about 13 weeks of work. That is exactly why fueling practice belongs at the start of a training block, not in the taper.
What a sweat-rate test is, and why you should do one
Weigh yourself nude and towelled dry immediately before a one-hour session, then again straight after; empty your bladder first, or the maths breaks. Add the litres you drank to the kilograms you lost — one litre of sweat weighs one kilogram, which is what makes the test work — and divide by the hours elapsed. That is your sweat rate. It varies more between athletes than any other input on this page, from under 0.5 L/h to over 2 L/h, which is why the population default of 0.9 L/h is a placeholder rather than an answer. Replace 60–80% of your losses, not 100%: drinking to full replacement across a long day is how athletes end up hyponatraemic, and the gut cannot absorb that much anyway. Test in conditions close to race day, because heat and humidity move the number substantially.