Carb Loading Calculator
Get exact daily carb targets, a day-by-day plan, and food examples sized to your body weight — for half marathons, full marathons, or endurance events beyond 26.2.
Select your event, enter your details, and get a protocol that matches your distance, not a generic chart someone pasted from a textbook.
Build your carb loading plan
Choose your event type first — the targets, duration, and food guidance all change depending on how long you'll be racing.
For most runners, a half marathon does not require the same 48–72 hour loading protocol used before a full marathon. That said, increasing carbohydrate intake meaningfully the day before — roughly 7–10 g/kg — can still top off glycogen stores and reduce the risk of fading in the final miles. Focus on familiar foods, reduce fiber in the final 12 hours, and eat a solid race-morning meal.
Your personalized carb loading plan
How to use this carb loading calculator
This tool is designed for any endurance runner who wants a personalized carbohydrate loading plan rather than a generic gram target from a blog post. It works for half marathons, full marathons, and ultra or endurance events beyond 26.2 miles.
Start by selecting your event type using the tabs at the top of the calculator — this is the most important input, because the protocol length, daily gram targets, and food guidance all change meaningfully depending on how long you'll be racing. Then enter your body weight, race date, dietary preference, and GI tolerance. Hit generate, and the calculator outputs a day-by-day carb loading schedule with exact gram targets, suggested foods, and training guidance for each day leading into your race.
The shareable URL captures all your inputs so you can bookmark your plan or send it to a coach. The CSV export gives you a version you can drop into a spreadsheet or print.
How carb loading differs by event
The right carb loading protocol depends entirely on race duration. Longer time on your feet means more glycogen depletion — and a bigger loading window to match.
| Event | Protocol | Target (g/kg/day) | Start loading | Fiber reduction |
|---|---|---|---|---|
| Half Marathon | 1-Day Top-Off | 7–10 g/kg | Day before race | Final 12 hours |
| Marathon | 48h High or 72h Gradual | 8–12 g/kg/day | 2–3 days before | Final 24–36 hours |
| 50K / Ultra | 72h Full Protocol | 10–12 g/kg/day | 3 days before | Final 36–48 hours |
| 100-Mile / Multi-Day | 72h+ with mid-race strategy | 10–12 g/kg/day pre-race | 3–4 days before | Final 48 hours |
How carb loading works
Carb loading is the process of systematically increasing carbohydrate intake before an endurance event to maximize the glycogen stored in your muscles and liver. When you exercise at race intensity, glycogen is the primary fuel — and when it runs out, pace drops hard.
The modern approach has moved well past the outdated depletion-then-load cycle. Current evidence supports a simpler protocol: taper training volume, raise carbohydrate intake sharply for 1–3 days depending on event length, keep foods familiar and low-fiber near race day, and arrive at the start line topped off rather than stuffed.
For a deep dive on the marathon-specific version, read the carb loading for marathon guide or use the dedicated marathon carb loading calculator.
What to expect during carb loading
The point of the whole exercise. Topped-off muscles mean more fuel available at race intensity before you have to slow down.
Glycogen binds roughly 3g of water per gram stored. A 2–4 lb gain is normal — it is fuel weight, not fat.
White rice, pasta, bagels, potatoes, cereal, sports drink. Race week is not the time to experiment with new foods.
Taper creates the room for glycogen supercompensation. Hard workouts during a load cancel much of the benefit.
Frequently asked questions
How do I use a carb loading calculator?
Select your event type, enter your body weight and race date, and choose a protocol. The calculator outputs your daily gram target, a day-by-day schedule, and food suggestions sized to your specific distance.
Should I carb load for a half marathon?
A single high-carb day the day before is enough for most half marathon runners. A full 48–72 hour marathon-style load is generally unnecessary, but one well-structured carb-loading day can still make a difference near the end of a hard effort.
How many carbs should I eat before a marathon?
Most marathon runners target 8–10 g/kg/day over 72 hours, or 10–12 g/kg/day over the final 48 hours. For a 70 kg runner that is roughly 600–840 grams of carbohydrate per day — spread across multiple meals.
Is carb loading different for ultra marathons?
Ultra runners generally use the full 72-hour protocol at the higher end of targets (10–12 g/kg/day). Given longer time on feet, extra attention to low-fiber choices and practiced race-morning fueling matters even more than at the marathon distance.
What foods are best for carb loading?
White rice, pasta, bagels, white bread, potatoes, bananas, cereal, pretzels, and sports drink. The theme is high carbohydrate, low fiber, and familiar — not gourmet.
Will carb loading cause GI problems?
It can if you introduce unfamiliar foods, eat too fast, or keep fiber too high near race day. Use this calculator's GI sensitivity setting and reduce fiber progressively in the final 24–36 hours to minimize the risk.
Carb loading is one piece. Get a plan that ties it all together.
Course-specific pacing strategy, heart rate zone training, 12–18 week schedule, and a race-day execution plan — built around your exact marathon and goal time.