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Endurance Nutrition & Fueling
Endurance nutrition calculators: daily calorie needs, carbohydrate grams per hour for long sessions, and your personal sweat rate for hydration. Free.
Daily Calorie Calculator
Your daily calorie need is your basal metabolic rate (BMR) multiplied by an activity factor, giving total daily energy expenditure (TDEE). A 35-year-old man, 70 kg and 175 cm, has a BMR near 1,624 kcal. Training at a moderate level (factor 1.55), he needs about 2,517 kcal a day to maintain weight.
Carbohydrate Intake Calculator
Fuel by duration. Under an hour, water is usually enough (0 g/h). From 1 to 2.5 hours, aim for about 60 g of carbohydrate per hour from a single source. Beyond 2.5 hours, you can absorb up to 90 g/h using a glucose-to-fructose mix near 2:1. A 2-hour session needs roughly 120 g total.
Sweat Rate Calculator
Your sweat rate is the fluid you lose per hour of exercise. Weigh yourself before and after a session, add any fluid you drank, and divide by the time. Lose 1 kg in an hour while drinking 500 ml and your sweat rate is 1.5 L/h. On long efforts, replace roughly 100% to 150% of it.
Which number do you actually need?
Endurance nutrition comes down to three separate questions: how much to eat across a day, how much to take in during a session, and how much to drink. Each has its own calculator and none of them substitutes for the others.
| Model | Anchored to | Best for | You need |
|---|---|---|---|
| Daily Calories | Mifflin-St Jeor resting metabolism × activity | A daily baseline to eat around, and to adjust from | Height, weight, age, sex and an honest activity level |
| Carb Intake | Grams of carbohydrate per hour of exercise | Fuelling sessions and races longer than about 90 minutes | Session duration and intensity |
| Sweat Rate | Body-weight change across a session | Building a personal drinking plan instead of a generic one | Weight before and after, and what you drank in between |
Swipe sideways for every column. Each answers a different question, so most athletes end up using all three.
The estimate is the starting point, your body is the feedback
Every calorie equation is a population average applied to an individual. Mifflin-St Jeor is the most accurate of the common formulas and still carries an error of roughly 10 percent for any given person, before you add the much larger uncertainty in how much your training actually burns.
Treat the number as a hypothesis. Eat around it for two weeks, track weight and, more importantly, how training feels, then adjust. Persistent fatigue, stalled sessions and poor sleep are usually an intake problem long before the scale says anything useful.
Your gut is trainable, and most athletes under-train it
Tolerating 90 grams of carbohydrate per hour is not something you either can or cannot do. Intestinal transporters upregulate with repeated exposure, so the ceiling moves if you practise deliberately in training rather than discovering it on race day.
Start at the low end of the range for your session length, use the same products you plan to race with, and add roughly 10 grams per hour every couple of weeks. The session that teaches your gut the most is the long one you fuel exactly as you intend to fuel the race.
Frequently asked questions
How many carbohydrates do I need per hour?
For efforts under about 90 minutes, 30 to 60 grams per hour is usually enough. Beyond that, 60 to 90 grams per hour supports harder and longer work, and trained guts using a glucose-fructose mix can go higher still. The right number is the most you can absorb comfortably, which is a figure you build in training.
Can I trust a calorie calculator?
As a starting point, yes. Resting metabolism from Mifflin-St Jeor is reasonably accurate, but the activity multiplier and the calorie cost of your training are far rougher, so the total can be off by several hundred. Use it to set a baseline and let two weeks of real feedback correct it.
How much should I drink during exercise?
Enough to limit losses to roughly two percent of body weight, which is where performance starts to fall measurably. That is personal: sweat rates range from under half a litre to more than two litres per hour depending on the athlete, the intensity and the heat, which is exactly why measuring your own is worth one session.
Should I train with low carbohydrate availability?
Some athletes use occasional low-carbohydrate sessions to push aerobic adaptations, but it is a targeted tool rather than a default. Doing it often compromises the quality of hard sessions, and the intensity you lose usually costs more than the adaptation gains. Keep hard days fully fuelled.
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