Triathlon Nutrition Calculator
Enter your weight, race distance, target finish time and race-day conditions to get a complete race-day nutrition plan. The calculator gives you total calories burned, how many carbohydrates and how much fluid you need per hour, estimated sodium losses, and a discipline-by-discipline feeding breakdown for the swim, bike, and run legs. All figures update instantly as you type.
How triathlon nutrition is calculated
The calculator uses the MET (Metabolic Equivalent of Task) method endorsed by exercise physiologists to estimate energy expenditure. Each discipline has an established MET value - swimming at race pace is approximately 8.0 kcal per kilogram per hour, cycling at race pace is approximately 8.0, and running is approximately 9.8. Multiplying MET by your body weight in kilograms and time in hours gives kilocalories burned for each segment. Carbohydrate recommendations follow the tiered guidance from Jeukendrup (2011): 30 g per hour for events under one hour, 60 g per hour for one to two and a half hours, and up to 90 g per hour for longer efforts when a glucose-fructose blend is used. Fluid targets of 500-900 ml per hour are based on consensus guidelines from the American College of Sports Medicine, scaled for temperature and sex. Sodium replacement of 500-1000 mg per hour reflects sweat sodium concentrations measured in endurance athletes.
Nutrition strategy by discipline
The swim leg is short and you cannot carry food, so focus on pre-race top-up: 20-30 g of carbohydrates from easily digested sources (a banana, a rice cake, or a dilute sports drink) roughly 30 minutes before the start. On the bike, your gut is far more tolerant of solid foods because you are seated and your core is stable. Aim for your target carbohydrate intake every 20 minutes: energy gels, bars or chews all work well, combined with a sports drink to co-deliver fluid and sodium. In the first half of the bike you can eat more substantial foods; switch to gels only from the midpoint to prime the gut for the run. The run is the hardest phase for eating because GI distress peaks when you are upright and moving. Stick to gels, chews, and sports drinks, avoid anything requiring significant chewing after the third kilometre, and keep sipping - even small 150-200 ml gulps at aid stations add up.
Hydration and electrolytes
Dehydration of as little as 2% of body weight reduces endurance performance measurably, yet over-drinking carries its own risk (hyponatraemia). The safe target is matching fluid losses without exceeding them. On moderate days (15-25 C) most athletes need around 700 ml per hour on the bike and run; hot conditions raise this to 900 ml per hour and cold conditions lower it to around 500 ml per hour. Female athletes typically sweat about 10% less per hour than male athletes at equivalent intensities, so the calculator adjusts downward accordingly. Sodium is the most important electrolyte to replace. Sweat sodium concentrations range from about 300 to 1800 mg per litre, averaging around 700-900 mg per litre in endurance athletes. A practical target of 700-1000 mg per hour - achieved through salted gels, electrolyte tablets, or formulated sports drinks - prevents the dilutional sodium drop that drives hyponatraemia. Do not rely on plain water alone for races over 90 minutes.
Pre-race and recovery nutrition
The 24-48 hours before your race is the carbohydrate loading window. Aim for 8-12 g of carbohydrates per kilogram of body weight on the final day. On race morning, eat a familiar high-carb, moderate-protein meal two to three hours before the start (oatmeal, white rice, or toast with a banana), followed by a small 20-30 g carbohydrate top-up 30 minutes out. In the 30 minutes after crossing the finish line, the GLUT-4 transporters in your muscle cells are at their most active, making glycogen synthesis fastest during this window. Target 1.2 g of carbohydrates per kilogram of body weight combined with 0.3 g of protein per kilogram. Chocolate milk, a commercial recovery drink, or a meal of rice with chicken all hit this ratio well. Prioritise fluid and sodium alongside food recovery.
Standard triathlon race distances
| Format | Swim | Bike | Run | Typical finish time |
|---|---|---|---|---|
| Sprint | 0.75 km (0.47 mi) | 20 km (12 mi) | 5 km (3.1 mi) | 1:00-1:30 h |
| Olympic | 1.5 km (0.93 mi) | 40 km (25 mi) | 10 km (6.2 mi) | 2:00-2:30 h |
| Half Ironman | 1.9 km (1.2 mi) | 90 km (56 mi) | 21.1 km (13 mi) | 4:30-6:00 h |
| Full Ironman | 3.8 km (2.4 mi) | 180 km (112 mi) | 42.2 km (26.2 mi) | 10:00-14:00 h |
Official distances used by World Triathlon and Ironman. Times are approximate median finish times for age-group athletes.
Frequently asked questions
How many calories do you burn in a triathlon?
It depends heavily on your body weight, race distance, and pace. A 70 kg athlete racing an Olympic-distance triathlon typically burns 1,200-1,600 kcal. A Full Ironman at the same weight can cost 6,000-9,000 kcal over 10-14 hours. The MET method gives a reasonable estimate: multiply 8-10 by your weight in kilograms by hours of exercise for each segment, then sum them.
How many carbs do you need per hour in a triathlon?
Research by Jeukendrup and colleagues shows that the gut can absorb roughly 60 g of carbohydrates per hour when relying on glucose alone. If you combine glucose and fructose in a 2:1 ratio (as in most modern formulated gels), absorption rises to about 90 g per hour. For shorter events under one hour, 30 g per hour is sufficient. The key is to train your gut at race-specific carbohydrate rates well before your event.
Can you eat solids during a triathlon?
Yes, during the bike leg. Because you are seated and your core is relatively stable, the stomach tolerates solid foods - bars, bananas, rice cakes - much better on the bike than on the run. During the run, the vertical movement and elevated heart rate reduce gastric emptying. Stick to gels, chews, and liquids on the run, and avoid solid foods past the first few kilometres.
How much should you drink during a triathlon?
Aim for 500-900 ml of fluid per hour on the bike and run, adjusted for temperature. Hot conditions (above 25 C) push toward the upper end; cool conditions allow the lower end. Sip every 5-7 minutes rather than drinking large volumes infrequently. Mixing electrolytes into at least some of your fluid supply helps retain the water you drink and prevents sodium dilution.
What should you eat and drink right after a triathlon?
Start recovery nutrition within 30 minutes of finishing. The target is 1.2 g of carbohydrates per kilogram of body weight plus 0.3 g of protein per kilogram. This is the glycogen resynthesis window, when muscle cells absorb glucose fastest. A 300 ml glass of chocolate milk, a commercial recovery shake, or rice with chicken are all practical options. Continue drinking fluid with electrolytes until your urine returns to a pale straw colour.
Does a female athlete need a different nutrition plan?
Partly. Female athletes generally have lower sweat rates than male athletes at the same relative exercise intensity, so fluid targets are typically about 10% lower. Total calorie needs are also lower at the same body weight because of differences in average muscle mass. Carbohydrate and sodium replacement guidelines are the same per kilogram. Hormonal fluctuations across the menstrual cycle can also affect substrate use and gut tolerance, so female athletes benefit from tracking nutrition in training across different cycle phases.
What is gut training and why does it matter for triathletes?
Gut training is the practice of consuming carbohydrates and fluids at race-level rates during training sessions to adapt the gastrointestinal tract. The gut is a trainable organ: repeated exposure to large carbohydrate doses increases SGLT-1 transporter density, improving absorption. Athletes who only eat gels in races without practising them in training are far more likely to experience nausea, bloating, or diarrhoea. Run at least three brick sessions using your exact race-day products at your target intake rates before your event.
Sources
- Jeukendrup AE. Nutrition for endurance sports: marathon, triathlon, and road cycling. Journal of Sports Sciences, 2011.
- Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 2016.
- Ainsworth BE et al. 2011 Compendium of Physical Activities. Medicine and Science in Sports and Exercise, 2011.