In a long triathlon you burn far more energy than you can absorb, so fuelling is about slowing the drain on your glycogen stores. Most of the eating and drinking happens on the bike, where your stomach handles it best.
How to use the Triathlon Nutrition Calculator
- Body weight
- Swim time – hours
- minutes
- seconds
- Bike time – hours
- minutes
- seconds
- Run time – hours
- minutes
- seconds
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter your weight and your expected swim, bike and run times for the race.
Tips
- Practise transitions – they count towards your total time.
- Train your race-day nutrition as carefully as your fitness.
- Heart rate zones differ slightly between swimming, cycling and running.
- Everything is calculated in your browser.
Common mistakes to avoid
- Going too hard on the bike and suffering on the run.
- Trying new food or gear on race day.
- Ignoring open-water skills.
Inputs explained
| Field | What to enter |
|---|---|
| Body weight | Units: kg, lb |
| Swim time – hours | A number |
| minutes | A number |
| seconds | A number |
| Bike time – hours | A number |
| minutes | A number |
| seconds | A number |
| Run time – hours | A number |
| minutes | A number |
| seconds | A number |
What each result means
- Swim calories = (8.3)×3.5×([Body weight])÷200×(([Swim time – hours]×3600 + [minutes]×60 + [seconds])÷60)
- Bike calories = (10)×3.5×([Body weight])÷200×(([Bike time – hours]×3600 + [minutes]×60 + [seconds])÷60)
- Run calories = (9.8)×3.5×([Body weight])÷200×(([Run time – hours]×3600 + [minutes]×60 + [seconds])÷60)
- Total calories burned = [Swim calories] + [Bike calories] + [Run calories]
- Fluid to drink (≈ 600 ml/h on bike and run) = (([Bike time – hours]×3600 + [minutes]×60 + [seconds]) + ([Run time – hours]×3600 + [minutes]×60 + [seconds]))÷3600×0.6
Example values
How the main result changes when Body weight changes and everything else stays at the example values above:
| Body weight (kg) | Total calories burned (kcal) |
|---|---|
| 35 | 2,026 |
| 52.5 | 3,039 |
| 70 | 4,052 |
| 87.5 | 5,065 |
| 105 | 6,078 |
| 140 | 8,105 |
Formula
Calories = MET × 3.5 × kg ÷ 200 × minutes (swim 8.3, bike 10, run 9.8 MET) · Carbs: 30–60 g/h (under 2.5 h) or 60–90 g/h (longer) · Fluid ≈ 400–800 ml/h
Worked example
Inputs — Body weight: 70 kg; Swim time – hours: 0; minutes: 40; seconds: 0; Bike time – hours: 3; minutes: 0; seconds: 0; Run time – hours: 2; minutes: 0; seconds: 0.
Results — Swim calories = 407 kcal; Bike calories = 2,205 kcal; Run calories = 1,441 kcal; Total calories burned = 4,052 kcal; Carbs to take during bike + run – from = 300 g; up to = 450 g; Fluid to drink (≈ 600 ml/h on bike and run) = 3 L; Equivalent energy gels (25 g each, mid estimate) = 15.
Key terms
- Glycogen
- Stored carbohydrate in muscles and liver.
Frequently asked questions
How many carbs per hour in an Ironman?
60–90 g per hour, using glucose plus fructose for the higher amounts.
Should I eat during the swim?
No – fuel before the start and on the bike.
How do I avoid stomach problems?
Practise your race nutrition in training.
Do I need salt?
Yes in long or hot races – 300–600 mg sodium per hour.