Race Fuel Planner: free carbs, fluid and sodium calculator.
Pick your race and finish time. Get carbs, fluid and sodium per hour, with the paper behind every number.
Your plan
70.3 (half distance) · 5 h 30 min
Carbs an hour
75g
The research range for this race is 60 to 90 g; your gut training sets where you start. Above 60 g, use glucose and fructose, about 2:1.
Jeukendrup 2014Viribay 2020+4 moreFluid an hour
Up to 1,300ml
Up to your sweat rate, never more. Add your weight to see the low end.
NATA 2017ACSM 2007Sodium an hour
300 to 1,000mg
Sweat sodium varies a lot between people. A sweat sodium test gives you your own number.
Baker 2017NATA 2017+1 moreLeg by leg (typical splits for this distance)
- Swim36 minNo fuel
- Bike2 h 48 min210 g carbs
- Run1 h 56 min145 g carbs
About 365 g of carbs over the race (bike and run). That is a 25 g gel every 20 minutes, or the same carbs from drink and chews. Fluid in total: up to 6,350 ml.
Rehearse it in training first: the gut adapts in 2 to 4 weeks. Costa 2017
Hand it to your AI
Your AI can check these numbers against your training and adjust them. The prompt has your results filled in.
See the prompt
I'm racing a 70.3 (half distance) and expect to finish in 5 h 30 min. My sweat rate is about 1,300 ml an hour. Conditions look mild, and my gut is in some training for fueling. A race fuel calculator built on the research (Jeukendrup 2014, the ACSM 2016 position stand) gave me: 75 g carbs an hour (glucose and fructose, about 2:1), about 365 g in total; up to 1,300 ml fluid an hour; 300 to 1,000 mg sodium an hour. Check this against my training and how my gut has handled fueling, then build my race day plan: what to take and when, leg by leg, with real products I can buy.
Gemini, Grok Bot, Dots, Muse and Cue: copy the prompt and paste it in.
With Memory.fit, your AI would already know your sweat rate.
On Android now: get it on Google Play. One email when the iPhone app is on the App Store.
How it works
How the Race Fuel Planner works.
Carbs per hour depend mostly on how long you race, not how hard. Under 30 minutes you need nothing. Up to 75 minutes a small amount or a mouth rinse is enough. From 75 minutes to 2 hours the research says 30 to 60 g an hour. Past 2 hours it is 60 to 90 g, and above 60 g you need glucose and fructose together, because one sugar on its own is absorbed at about 60 g an hour at most.
Where you land in the range depends on your gut. A gut that is new to fueling starts at the bottom; a trained gut can take the top. Gut training takes 2 to 4 weeks of practice in training.
Fluid comes from your sweat rate. The goal is to lose less than 2% of your body weight over the race, and never to drink more than you sweat. Without a sweat rate the research says drink to thirst, so the planner gives you no made up number. Sodium matters from about 2 hours: 300 to 1,000 mg an hour, or your sweat rate times your sweat sodium if you have tested it.
The formula
- carbs per hour = the band for your race duration, set by your gut training
- fluid per hour = between (sweat rate × hours − 2% of body weight) ÷ hours and your sweat rate
- sodium per hour = sweat rate (l/h) × sweat sodium (mg/l), at most 1,000 mg
The science
Where the numbers come from.
These are the same rules Memory.fit's engine uses when your AI asks it for a number, read from one registry of cited sources.
Jeukendrup A. A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise (2014). Sports Medicine 44(Suppl 1):25-33.
Review · 2014 · doi:10.1007/s40279-014-0148-z
Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance (2016). Medicine & Science in Sports & Exercise 48(3):543-568.
Position stand · 2016 · doi:10.1249/MSS.0000000000000852
Jeukendrup AE. Carbohydrate and exercise performance: the role of multiple transportable carbohydrates (2010). Current Opinion in Clinical Nutrition and Metabolic Care 13(4):452-457.
Review · 2010 · doi:10.1097/MCO.0b013e328339de9f
Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine Position Stand: Exercise and Fluid Replacement (2007). Medicine & Science in Sports & Exercise 39(2):377-390.
Position stand · 2007 · doi:10.1249/mss.0b013e31802ca597
Baker LB. Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability (2017). Sports Medicine 47(Suppl 1):111-128.
Review · 2017 · doi:10.1007/s40279-017-0691-5
Example
A worked example.
A 75 kg triathlete racing a 70.3 in 5:30, sweat rate 900 ml an hour, mild weather, gut in some training.
- 15:30 is past 3 hours, so the band is 60 to 90 g of carbs an hour. Some gut training puts the target in the middle: 75 g an hour, as glucose and fructose.
- 2The swim takes about 36 minutes and you can't eat there, so the carbs go on the bike (about 210 g) and the run (about 145 g). That is a 25 g gel every 20 minutes, or the same carbs from drink and chews.
- 3Losing less than 2% of 75 kg means losing at most 1.5 kg. Sweating 900 ml an hour for 5.5 hours, that means drinking 700 to 900 ml an hour on the bike and run.
- 4No sweat sodium test, so the range applies: 300 to 1,000 mg of sodium an hour, nearer the top if it turns hot.
Questions
Race Fuel Planner: questions.
For a marathon over 2 hours the research says 60 to 90 g an hour, as glucose and fructose above 60 g. Under 2 hours, 30 to 60 g. Start at the bottom if your gut isn't used to it, and practice your race fueling on long runs.
Up to about 60 g an hour, any fast carbohydrate works. Above that, your gut absorbs glucose on its own at about 60 g an hour, so the research uses glucose and fructose together, around 2:1, to reach 90 g and beyond.
Enough to lose less than 2% of your body weight over the race, and never more than you sweat. The only way to know that number is a sweat test. Without one, the research says drink to thirst.
For races over 2 hours the research range is 300 to 1,000 mg an hour. Sweat sodium varies a lot between people, so a sweat sodium test gives you your own number: sweat rate times sweat sodium.
Yes. Studies show 2 to 4 weeks of regular fueling in training raises how much you absorb and lowers stomach trouble. Rehearse your race intake in long sessions, never for the first time on race day.
Because a fluid number without your sweat rate is a guess, and guessing too high is how athletes overdrink. Do the sweat rate test once and the planner gives you a range.
Not medical advice. These numbers come from published research on groups of athletes. Your own needs can differ; talk to a doctor or a sports dietitian about any health condition.