Timeline
Hour-by-hour targets
Carbohydrate, fluid, sodium, and caffeine targets for each hour or race segment.
Race Nutrition Calculator for Marathon, Ironman & Ultras
Build an EnduranceOS Fueling Blueprint with hour-by-hour carb, fluid, sodium, and caffeine targets tailored to your body, race, and expected conditions.
What you enter
Race, target time, body details, experience, location, weather, and the fuel formats you prefer.
What you get
A Fueling Blueprint with hour-by-hour carb, fluid, sodium, caffeine, and product targets.
Your plan
What your Fueling Blueprint includes
Fuel
Practical combinations
Gels, chews, drink mix, or real-food suggestions matched to your preferences.
Conditions
Weather context
Fluid and risk guidance adjusted for temperature and humidity at your race location.
Race day
Totals and reminders
Race totals, pre-race notes, risk flags, and a plan you can save or export.
Nine race types
Built for endurance race day
Triathlon
- Ironman 140.6
- Ironman 70.3
Running
- Marathon
- Ultra 50K
- Ultra 50 Mile
- Ultra 100K
- Ultra 100 Mile
Cycling
- Century Ride
- Gran Fondo
Method
How your targets are estimated
The calculator turns published endurance-nutrition ranges into a practical starting point for your race. A formula cannot replace what you learn by testing the plan in training.
- Carbohydrate
- Uses race energy demand within experience-based gut-tolerance ranges, with an easier first hour and late-race adjustments for longer events.
- Fluid
- Starts with a measured or estimated sweat rate, adjusts for conditions, and keeps the target within practical hourly intake limits.
- Sodium
- Combines sweat rate with your self-reported salt-loss tier and recommends partial replacement rather than automatically replacing every milligram lost.
- Caffeine
- Builds a body-weight-based budget and changes the timing for shorter races, long events, and overnight ultras.
Before you begin
What you need to get started
- Race: distance, target finish time, date, start time, and location.
- Body: weight, age, sex, experience, and how heavily you tend to sweat.
- Preferences: gels, chews, drink mix, real food, or a combination.
- Optional refinements: measured sweat rate, cycling power, salt-loss signs, and cramping history.
Research library
Go deeper on the science
CarbohydrateHow Many Carbs Per Hour for an Ironman?How race duration, energy demand, and gut training shape hourly carbohydrate targets.FluidHow to Calculate Your Sweat RateA field-test method for replacing an estimate with your measured sweat rate.SodiumHow Much Sodium Do You Need Per Hour?A practical explanation of sweat sodium loss and partial replacement targets.CaffeineCaffeine Timing for Endurance RacesHow total dose and timing change between shorter races and overnight ultras.
Questions
Frequently Asked Questions
Is the race nutrition calculator free?
Yes. You can build race nutrition plans for free, with no account required to use the calculator.
Which race distances does the calculator support?
It supports Ironman 140.6, Ironman 70.3, marathon, 50K, 50-mile, 100K and 100-mile ultras, century rides, and gran fondos.
How does the calculator estimate carb, fluid, and sodium targets?
It combines your race type and target time with body weight, experience, weather, estimated or measured sweat rate, and self-reported salt-loss indicators. The results are practical starting points to test and adjust in training.
What information do I need before I start?
Have your race distance, expected finish time, body weight, race date, and location ready. A measured sweat rate, cycling power, and notes about how heavily you sweat or whether you see salt residue are optional refinements.
Does the calculator include caffeine timing?
Yes. The Fueling Blueprint estimates a total caffeine budget from body weight and schedules it differently for shorter races, long races, and overnight ultras. Adjust it for your tolerance and what you have tested in training.
Is this medical or dietary advice?
No. The calculator provides sports-nutrition estimates, not medical or dietary advice. Individual needs vary, and every plan should be tested in training before race day.