Marathon Carb Loading Calculator
Build your personalized 48-72h carb loading plan to maximize glycogen stores and sustain goal pace longer
Science-backed, no-depletion protocol with daily gram targets (8-12 g/kg) — improvements are typically modest but meaningful in set-distance events
🏃 Want a Complete Marathon Strategy?
Get a personalized training plan with carb-loading guidance, race-day fueling strategy, and course-specific pacing—all integrated for your goal race.
Build My Training Plan ($19) →Use this free marathon carb-loading calculator to plan a modern, no-depletion carbohydrate loading protocol. Carb-loading increases glycogen so you can hold goal pace deeper into the race; in set-distance events, improvements are typically modest but meaningful (~2-3% in time trials). Set carb targets by body weight (g/kg), align with your taper, and learn exactly how many grams of carbs to eat before a marathon to maximize glycogen and avoid "the wall."
Updated: January 2025 | Author: Pace Perfect Sports Science Team | Review: Sports Dietitian reviewed | Methodology: Based on Burke et al. sports nutrition research and ACSM guidelines | For educational purposes; consult healthcare providers for medical advice.
Personal & Race Details
Why Carb Loading Works for Marathon Performance
Carbohydrate loading increases muscle glycogen stores and helps you sustain goal pace longer. Well-trained athletes can super-compensate without a depletion phase. This translates to:
Improved Endurance
Hold goal pace deeper into the race; typical gains are modest but meaningful in marathons
Consistent Pacing
Avoid "hitting the wall" and maintain goal pace
Mental Clarity
Stable blood glucose for decision-making
Glycogen + Water
Expect 1-2% body-mass increase—this is normal and helpful
Our Science-Based Protocol
Our calculator follows the proven "taper and increase" method backed by Burke et al. research. This modern approach avoids the outdated depletion phase while maximizing glycogen storage through strategic carbohydrate timing and training reduction. Modern loading doesn't require depletion; taper + high carbs achieve super-compensation (even 24–48h can work in trained athletes).
What You'll Get:
- 48-72h personalized plan with daily carb targets (8-12g/kg body weight)
- Pre-race meal guidance: Plan 1–4 g/kg 1–4h before the gun; adjust for GI comfort
- Food recommendations tailored to your dietary needs
- Shareable URL to save and share your exact plan
- Printable/exportable format for race week
Key Benefits:
- No depletion phase required
- Low-fiber & Low-FODMAP options
- Evidence-based carb targets
- Weight change estimator (1-2% normal)
- Coordinated with training taper
📊 Methods & Evidence Panel (click to expand)
Calculations Used:
- Daily carbs (g) = mass_kg × target g/kg
- Pre-race meal = 1–4 g/kg @ T−3–4 h before start
- Weight change estimator = Δmass ≈ added glycogen (g) × 3–5 / 1000 kg
- Each gram of glycogen binds ~3g water → expect ~1–2% body-mass increase (normal and helpful)
Evidence Ranges:
- 48h High protocol: 10–12 g/kg/day for final 36–48h before race
- 72h Gradual protocol: 8–10 g/kg/day for final ~72h before race
- Pre-race meal: 1–4 g/kg consumed 1–4h before start (adjust for GI comfort)
- Fiber limit: <15–20g on final day to minimize GI distress
- Weight gain: Each gram of glycogen binds ~3g water → expect ~1–2% body-mass increase
Key References:
- Burke et al. (2011) - Carbohydrate loading guidelines, J Sports Sci
- ACSM Position Stand (2016) - Nutrition and Athletic Performance
- Jeukendrup (2014) - Sports nutrition and glycogen supercompensation
- Hawley et al. (1997) - Carbohydrate-loading and exercise performance
- Sherman et al. (1981) - Effect of exercise-diet manipulation on muscle glycogen
Last Updated: January 2025 | Reviewed by: Sports Nutrition Science Team
🍞 Carb Building Blocks (Food Translator)
Use these common foods to hit your daily targets. Each item shows approximate carb content:
High-Carb Staples:
- 1 bagel ≈ 50g carbs
- 1 cup cooked white rice ≈ 45g carbs
- 1 cup cooked pasta ≈ 40g carbs
- 1 large banana ≈ 25–30g carbs
- 500ml sports drink ≈ 30g carbs
- 2 slices white bread ≈ 30g carbs
Quick Energy Sources:
- 1 energy gel ≈ 25g carbs
- 1 medium sweet potato ≈ 25g carbs
- 250ml fruit juice ≈ 30g carbs
- 1 granola bar ≈ 25g carbs
- 2 pancakes (4" diameter) ≈ 30g carbs
- 1 cup oatmeal (cooked) ≈ 30g carbs
💡 Pro tip: Vegan/gluten-free swaps are automatically included in your personalized plan based on dietary preferences
🚨 Important Reminders
- Practice first: Test your carb loading strategy during training, not for the first time on race week
- Weight gain is normal: Each gram of glycogen binds ~3g water → expect ~1–2% body-mass increase (normal and helpful for performance, not fat gain)
- Reduce fiber: Aim for <15-20g fiber in the final 24 hours to minimize GI distress
- Pre-race meal timing: Plan 1-4 g/kg carbs 3-4 hours before the gun
- Stay hydrated: Increased carb intake requires additional water consumption
- Time your meals: Eat your largest carb meal at lunch, lighter dinner for better sleep
💡 Advanced Carb Loading Tips
Food Selection Strategy:
- High-carb, low-fiber: White rice, pasta, bagels, pretzels
- Quick energy: Bananas, sports drinks, honey
- Avoid: Whole grains, beans, cruciferous vegetables
Timing Considerations:
- Meal frequency: 5-6 smaller meals vs. 3 large meals
- Evening strategy: Light dinner to ensure good sleep
- Race morning: 3-4 hours before start time
🎯 Ready for Your Complete Marathon Strategy?
Carb-loading is just one piece of the puzzle. Get a personalized training plan that includes:
Integrated with your taper
Hour-by-hour carb strategy
Mile-by-mile adjustments
Personalized to your fitness
💯 30-day money-back guarantee
Frequently Asked Questions
Will I feel sluggish from extra carbs?
You may notice mild water retention (2-4 lbs), but this is beneficial glycogen-bound water that will fuel your performance. Most runners feel energized, not sluggish.
Can I carb-load on a plant-based diet?
Absolutely! Our calculator provides specific recommendations for vegetarian/vegan diets using rice, potatoes, fruits, and low-fiber grains.
What if I have a sensitive stomach?
We recommend smaller, more frequent meals and emphasize low-fiber carb sources to minimize GI distress. Always test during training first.
How does this differ from old-school carb loading?
Modern carb loading eliminates the harmful depletion phase. You simply reduce training while increasing carbs - much easier and more effective.
📚 Methodology & Sources
Our calculator is based on peer-reviewed sports nutrition research and position stands from leading organizations:
- Burke, L.M., et al. (2011) - Carbohydrate loading guidelines from the Journal of Sports Sciences
- ACSM Position Stand (2016) - Nutrition and Athletic Performance recommendations
- Jeukendrup, A.E. (2014) - Sports nutrition research on glycogen supercompensation
This tool provides educational information based on current sports science. Always consult with healthcare providers or sports nutritionists for personalized medical advice.
Complete Your Race Preparation
Maximize your marathon performance with our full suite of science-backed tools:
🥤 Marathon Fueling Calculator
Calculate your hourly carb and fluid needs during the marathon
⏱️ Marathon Pacing Calculator
Determine your optimal race pace and split times