Carbohydrate Timing Calculator
Plan your race day nutrition strategy with personalized carbohydrate recommendations based on your body weight, race distance, and individual tolerance.
Carb timing vs carb loading: this calculator covers on-race fuelling (how many carbs per hour during the race). If you need a 3-day pre-race loading plan, use the Carb Loading Calculator instead.
When should you take carbs during a triathlon?
Start fuelling within the first 15–20 minutes on the bike and take a gel every 20–30 minutes from then on. Waiting until you feel hungry or low is already too late — the stomach shuts down as effort rises, so carbs consumed late sit there. A steady 60–120 g/hr schedule from T1 onwards is what works.
- Pre-race: 50–80 g carbs 2–3 hours before the swim
- Bike leg: one gel every 20–25 min, drink mix sipped continuously
- Run leg: gel every 25–30 min — reduce if GI feels rough
- Last 15 min of race: stop — no digestion time left
Calculator Input
Your Carbohydrate Plan
Enter your data and calculate to see results
Important Notes
- •Always test your nutrition plan in training before race day
- •Mix carbohydrate sources (glucose, fructose) for better absorption
- •If new to carb-loading, gradually increase your intake during training
Carbohydrate Timing Science
Proper carbohydrate timing can significantly improve performance in endurance events. Research shows that carbohydrate intake before and during exercise helps maintain blood glucose levels, spares muscle glycogen, and delays fatigue.
Key Principles
- Pre-race carbohydrate loading helps maximize muscle glycogen stores
- Multiple transportable carbohydrates (glucose + fructose) can increase absorption up to 90g/hour
- Carb intake during exercise should be matched to exercise intensity and duration
- Individual tolerance varies and can be improved through training
Scientific References
- Jeukendrup, A. (2014). "A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Medicine.
- Stellingwerff, T., & Cox, G. R. (2014). "Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations." Applied Physiology, Nutrition, and Metabolism.
- Currell, K., & Jeukendrup, A. E. (2008). "Superior endurance performance with ingestion of multiple transportable carbohydrates." Medicine and Science in Sports and Exercise.
Example calculation
Athlete: 75 kg triathlete, 70.3 race (6 h), moderate intensity, moderate tolerance.
Carbs per hour: 60 g/hr on the bike, ~48 g/hr on the run.
Pre-race (3 h out): ~150 g carbs (bagel + banana + oats).
On-course total: 60 × 3 (bike ~3h) + 48 × 2 (run ~2h) = ~276 g.
Practical mix: 1 gel every 20–25 min on bike, sports drink sipped continuously, gel every 30 min on the run.
Common mistakes
- Waiting until you feel hungry — by then the stomach won't accept carbs
- Taking all carbs as gels with plain water — causes GI distress; mix with drink for smoother absorption
- Stacking caffeine gels early on the bike — save caffeine for the run where it helps most
- Trying to hit 90+ g/hr without gut training — start at 60 g/hr and build week over week
- Still fuelling in the last 15 min of a race — no time to digest, skip it
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How this calculator works
Carb intake per hour is set by race distance and tolerance, then split across pre-race fueling, bike leg and run leg with caffeine layered on the run.
Assumptions
- • Multiple-transportable carb sources (glucose + fructose) for high intakes
- • Caffeine introduced on the run leg, not the bike
- • 15-minute fueling intervals for the bike, smaller doses on the run
Limitations
- • Always rehearse fueling at race pace before race day
- • Heat and altitude can reduce GI tolerance — start lower
- • Caffeine sensitivity varies — test in training
Who this is for
- • Triathletes building a race-day fueling timeline
- • Athletes training their gut to handle higher carb intake
- • Anyone troubleshooting late-race bonking or GI issues
Who this is not for
- • Athletes with diagnosed GI conditions — work with a sports dietitian
- • Pure sprint racers — minimal in-race fueling needed
Carb Timing Calculator FAQ
Scientific References
Comprehensive review of endurance nutrition needs
Detailed analysis of carbohydrate needs in sports
Related Articles
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