How many grams of carbs, how much fluid and how much sodium per hour on race day, from your finish time, the heat and how much you sweat.
h:mm, for example 5:30
Optional. Use the sweat rate calculator.
Carbs per hour
90 g on the bike, 60 g on the run
Start eating 15 to 20 minutes into the bike, then little and often. Practise this exact plan in training first.
The carb target climbs with the length of the race, because the longer you go the more of your energy has to come from what you eat rather than what you stored. The ladder follows Jeukendrup's 2014 review: small amounts for about an hour, up to 30 g per hour for one to two hours, up to 60 g for two to three hours, and up to about 90 g for the longest events, taken as a glucose and fructose mix so the gut can absorb it. For an athlete who has not trained their gut the calculator uses 80 g per hour on a long race, a little under that ceiling.
Some athletes train their gut to take more, so if you have practised 80 g or more per hour in training the calculator goes up to 110 g on the bike. That is above the 90 g in the review and is an estimate, so build up to it in training. The run gets less than the bike in a Half or a Full because many athletes tolerate less while running. That split is common practice and our estimate, not a figure from the review.
The ACSM position stand aims to prevent a loss of more than 2 percent of body weight, and 0.4 to 0.8 litres an hour is the typical drinking range commonly quoted from it, not a rule for everyone. Heat and a heavy sweat push the number up. The calculator never goes above 1 litre an hour, our own cautious ceiling, because drinking more than you sweat is what causes low blood sodium.
Sodium is counted per litre you drink. In a dataset of 506 athletes the average whole-body sweat sodium was about 800 mg per litre, with a range from roughly 400 to 1,600. The calculator uses 500, 700 or 1,000 mg per litre as estimates inside that range, and a heavy or salty sweater (white salt marks on your kit) gets the top one. The most accurate fluid number comes from your own sweat rate: weigh yourself before and after a session with the sweat rate calculator.
A typical gel holds 20 to 25 g of carbs, a bottle of sports drink 30 to 80 g depending on the mix, a bar 25 to 45 g. Count what the aid stations hand out and carry the rest.
The gel calculator splits the total into gels for the bike and the run, and the packing list makes sure they end up in the right bag.
Most athletes aim for 60 to 90 g of carbs per hour on the bike and a little less on the run. Some athletes train their gut to take more, up to around 110 g per hour, but the evidence is thinner above 90 g, so treat that as an advanced option. Practise the exact amount in training before race day.
For a race of four to six hours, 60 to 90 g per hour is the usual target, most of it on the bike. For a race under about two hours, around 30 g per hour is the usual target.
A typical range quoted from the ACSM position stand is 0.4 to 0.8 litres per hour, more in the heat or if you sweat heavily. As a cautious rule, do not drink more than about 1 litre per hour, and measure your sweat rate in training to get your own number.
This is an estimate: about 200 to 1,000 mg per hour depending on how much you drink and how salty your sweat is, since sweat sodium varies about fourfold between athletes. Salty sweaters, who finish with white marks on their kit, sit at the top of that range.
Start 15 to 20 minutes into the bike, once your breathing has settled after the swim, then eat little and often every 15 to 20 minutes rather than a lot at once.
