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IN-RIDE FUELLING CALCULATOR

Personalised carb, fluid, and sodium targets calculated from your actual watts, session type, and local weather. Based on Jeukendrup, Morton, and Romijn.

Session type determines what fraction of energy comes from carbs vs fat (Romijn et al. 1993). Combined with your watts, this gives a precise carb burn rate.

Steady aerobic riding. Mixed fat and carb oxidation.

Your expected average power for this session. A Z2 ride at 100W needs very different fuel than Z2 at 300W.

How practiced is your gut at absorbing carbs during exercise? This sets your absorption ceiling (Jeukendrup, 2014).

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Quick answer

Tell the calculator how long you're riding, how hard, your body weight, how trained your gut is, and the weather. It returns carbs per hour, total carbs, fluid per hour, sodium, glucose:fructose split, and a feeding interval based on Jeukendrup, Morton, and ACSM data.

WHAT IT DOES

Most amateur riders bonk because they under-fuel — they ride on what worked at lower intensities, then surprise themselves when they crack at hour three. This calculator gives you a specific carb, fluid, and sodium target for the actual ride you're doing, not a generic "60 g per hour" rule.

WHO IT'S FOR

  • →Anyone riding longer than 90 minutes who wants to finish strong
  • →Riders preparing for a sportive, gran fondo, or stage race
  • →Cyclists training their gut to handle higher carb intakes
  • →Athletes whose ride performance falls off a cliff in heat

HOW IT WORKS

We blend three frameworks: James Morton's "fuel for the work required" (carb intake scales with intensity), Asker Jeukendrup's dual-transporter model (glucose and fructose use separate transporters, allowing absorption above 60 g/hr), and ACSM/Sawka guidance on fluid and sodium. The result is a per-session prescription, not a generic recommendation.

  1. 01

    Pick the session profile

    Choose the closest match: recovery, endurance, tempo, sweet spot, threshold, VO2, race, or mixed intervals. Carb demand scales sharply with intensity.

  2. 02

    Enter ride duration and weight

    Duration in minutes; body weight in kg. Lighter riders need fewer total carbs; longer rides need feeding earlier.

  3. 03

    Set gut training honestly

    None / Some / Trained. If you're new to high-carb fuelling, start at the lower end of the range and build up over 4-6 weeks of training rides.

  4. 04

    Add weather

    Temperature and humidity drive sweat and sodium loss. Above 25°C in humid conditions, fluid needs can double.

  5. 05

    Execute on the bike

    Start fuelling within the first 30 minutes. Use the suggested feeding interval and respect the dual-transport split if you're above 60 g/hr.

EXAMPLE CALCULATIONS

75kg rider, 4hr endurance ride, 22°C, gut moderately trained

  • · Duration: 240 min
  • · Session: endurance
  • · Weight: 75kg
  • · Gut: some
  • · Temp: 22°C

60 g carbs/hr (240 g total), 600 ml fluid/hr, 500 mg sodium/hr, single-source glucose works.

70kg racer, 5hr sportive with surges, 28°C humid, gut trained

  • · Duration: 300 min
  • · Session: race
  • · Weight: 70kg
  • · Gut: trained
  • · Temp: 28°C

100 g carbs/hr (500 g total) using 2:1 glucose:fructose, 850 ml fluid/hr, 800 mg sodium/hr, feeding every 15 min.

LIMITATIONS

Carb absorption is highly individual — published ceilings (90-120 g/hr) assume a trained gut and the right glucose:fructose ratio. Sodium needs vary 4-fold across athletes. The calculator estimates from population averages and won't match a sweat patch test. Treat the output as a starting prescription you refine with experience.

When to see a coach

If you've followed the recommendations and still bonk, GI distress is consistent, or your weight drops more than 2-3% during a ride despite drinking — get a sweat patch test and speak to a sports nutritionist. Some riders have unusually high sodium losses or fructose intolerance that this calculator can't see.

FREQUENTLY ASKED QUESTIONS

How many carbs per hour should I eat on the bike?+

It depends on intensity and how trained your gut is. Easy rides (<2 hours): 30-40 g/hr or nothing. Endurance (2-4 hours, Z2-Z3): 60-80 g/hr. Threshold and racing (4+ hours or hard): 90-120 g/hr if your gut is trained. Below 60 g/hr, glucose alone is fine; above that, use a 2:1 glucose:fructose mix to use both intestinal transporters.

What is gut training in cycling?+

Gut training is the practice of progressively eating more carbs during training rides so your gut adapts to absorb them under exercise. The intestinal sodium-glucose transporter (SGLT1) and the fructose transporter (GLUT5) both upregulate with repeated high-carb training. Untrained gut: target 40-60 g/hr. Trained gut: 90-120 g/hr is achievable.

How much fluid should I drink per hour cycling?+

500-1000 ml per hour depending on temperature, humidity, body size, and individual sweat rate. ACSM guidance is to limit weight loss during exercise to under 2% of body weight. Sip continuously rather than gulping every 30 minutes. In hot conditions, pre-cooling and continuous fluid intake matter more than total volume.

Why do I bonk on long rides?+

Almost always because total carbohydrate intake doesn't match work done. Glycogen stores at ~500 g (2000 kcal); a 4-hour ride at endurance pace can burn 2400-3200 kcal, with carbs supplying 50-85% of energy depending on intensity. If you're eating a banana and a gel and call it fuelled, you're running an energy deficit by hour two.

What is the dual-transporter model?+

Glucose is absorbed via SGLT1 — capped around 60 g/hr. Fructose uses GLUT5 — adds another ~30-40 g/hr capacity. Combining the two in a roughly 2:1 glucose:fructose ratio lets athletes absorb 90-120 g/hr without gut distress. Most performance gels and drinks designed for endurance now use this ratio.

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