How many days should you carb load before a marathon?

Three days for a marathon or longer, and two days for a half marathon. Pierce Showe recommends a 3-day carb load for marathons and ultras because it's much easier to hit your daily target over three days than to cram it into two.

Which races should you carb load for?

Carb load for any race a half marathon or longer: a 2-day load for a half marathon, and a 3-day load for a marathon or ultramarathon. For shorter races, a normal high-carb diet is enough.

Carb Loading Calculator for Marathons and Ultramarathons

Q: How many carbs should I eat when carb loading?

For a 3-day carb load, aim for about 8–10 grams of carbohydrate per kilogram of body weight per day. For a 2-day load, aim for about 10–12 g/kg per day. A 150 lb (68 kg) runner doing a 3-day load would eat roughly 545–680 g of carbs per day.

Body weight

lb kg

Race

Carb load length

3 days

2 days

0 g

carbs per day (aim for)

0–0 g

daily range

0 g

total over 3 days

What that looks like

Pick foods that are almost all carbs, with little fat, protein or fiber. Here are some of my go-tos. Mix and match them across your meals and snacks to hit your daily target. Drinking some of your carbs (juice or a carb drink mix) is easier on your stomach than eating it all:

Food	Carbs per serving

Enter your weight to see your numbers.

How the calculator works

It uses the carb loading ranges from sports nutrition research:

3-day load: 8–10 g of carbs per kg of body weight per day (International Society of Sports Nutrition).
2-day load: 10–12 g of carbs per kg of body weight per day (International Olympic Committee).

"Aim for" is the middle of the range. For a marathon or longer, I recommend a 3-day carb load. It's much easier to hit your target spread over three days than to cram it into two. For a half marathon, I recommend a 2-day load.

Who should carb load?

Carb loading matters for any race a marathon or longer. It tops off your glycogen stores so you can hold your pace and push back fatigue on race day. For a half marathon, a shorter 2-day load is the way to go. For races shorter than a half, a normal high-carb diet is enough.

Want my exact plan, including what I eat in a 660-gram day? Read how I carb load to run 100 miles.

Want a custom carb loading plan?

DM me "CARB LOAD" on Instagram and we'll build yours together, or apply for coaching and I'll dial in your fueling for your whole training block and race day.

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This calculator is for general education, not medical advice. If you have diabetes or any medical condition, talk with your doctor or a registered dietitian before carb loading.

Common questions

How many carbs should I eat when carb loading?

For a 3-day load, about 8–10 g per kg of body weight per day. For a 2-day load, about 10–12 g/kg per day.

How many days should I carb load before a marathon?

Three days for a marathon or longer, because it's much easier to hit your target that way. For a half marathon, two days.

Which races should I carb load for?

Any race a half marathon or longer: 2 days for a half, 3 days for a marathon or ultra. For shorter races, a normal high-carb diet is enough.