Carb Loading Calculator

Carb Loading Calculator: How Many Carbs Should You Eat Before a Marathon or Endurance Race?

Carb loading is one of the most established nutrition strategies in endurance sports, but many athletes still have the same question before race day:

How many carbohydrates should I actually eat?

Eating a big bowl of pasta the night before a marathon is not necessarily enough.

Successful carbohydrate loading involves consuming a high carbohydrate diet for roughly 36 to 48 hours before a long endurance event so your muscles can begin the race with high glycogen stores.

Our free Carb Loading Calculator makes the math easy by using your body weight, race duration, and loading period to estimate your carbohydrate needs.

TLDR

For endurance events lasting longer than approximately 90 minutes, athletes can maximize muscle glycogen by consuming roughly 10 to 12 grams of carbohydrate per kilogram of body weight per day for 36 to 48 hours before competition.

A 160 pound athlete weighs approximately 73 kilograms. At 10 to 12 grams per kilogram, that works out to roughly 730 to 875 grams of carbohydrate per day during an aggressive carb load.

That may sound like a lot, and it is. Spreading carbohydrates across meals, snacks, sports drinks, and other easily digested carbohydrate sources can make the target considerably easier to reach.

Use our Carb Loading Calculator to determine a personalized target based on your body weight and race.

What Is Carb Loading?

Carbohydrate loading is a nutrition strategy designed to maximize the amount of glycogen stored in your muscles before prolonged exercise.

When you eat carbohydrates, some of that carbohydrate is converted to glucose and stored as glycogen in your muscles and liver.

During endurance exercise, muscle glycogen becomes an important source of energy.

The longer and harder you exercise, the more important carbohydrate availability can become.

Eventually, glycogen stores can become depleted enough that maintaining your previous exercise intensity becomes increasingly difficult.

Carbohydrate loading attempts to begin the race with as much glycogen available as practical.

Does Carb Loading Actually Work?

Carbohydrate loading is one of the better established strategies in endurance sports nutrition.

Research and sports nutrition guidelines indicate that increasing carbohydrate availability before prolonged endurance exercise can increase muscle glycogen stores and help athletes maintain their desired exercise intensity longer before fatigue becomes limiting.

Modern carb loading is also considerably simpler than many older protocols.

Athletes were once advised to perform a glycogen depleting workout followed by several days of low carbohydrate eating before dramatically increasing carbohydrate intake.

That depletion phase is generally unnecessary.

Instead, a well trained endurance athlete can taper training while consuming a high carbohydrate diet during the final 36 to 48 hours before competition.

How Many Carbs Should You Eat When Carb Loading?

For long endurance events, a commonly recommended target is:

10 to 12 grams of carbohydrate per kilogram of body weight per day

for approximately:

36 to 48 hours before competition

This amount is substantially higher than many athletes normally eat.

Example for a 160 Pound Runner

A 160 pound runner weighs approximately 72.6 kilograms.

At 10 grams per kilogram:

72.6 × 10 = 726 grams of carbohydrate per day

At 12 grams per kilogram:

72.6 × 12 = 871 grams of carbohydrate per day

That gives our runner a target of approximately:

725 to 870 grams of carbohydrate per day

during the final 36 to 48 hours before a long race.

Do You Need To Carb Load Before Every Race?

No.

Aggressive carbohydrate loading is most useful for events where glycogen availability is likely to become a meaningful performance limitation.

That generally means prolonged exercise lasting longer than approximately 90 minutes.

Examples include:

Marathons.

Ultramarathons.

Long trail races.

Long cycling races.

Long distance triathlons.

Long cross country ski races.

Long endurance competitions.

If your race lasts 30 or 60 minutes, consuming 10 to 12 grams of carbohydrate per kilogram for two days is unlikely to provide the same benefit.

Your normal carbohydrate rich diet and an appropriate pre-race meal may be sufficient.

How Long Should You Carb Load?

A practical modern carbohydrate loading protocol generally lasts:

36 to 48 hours.

You do not necessarily need an entire week.

During this period, training volume is normally reduced as part of your taper while carbohydrate intake increases.

That combination is important.

Heavy training continues to use glycogen, while tapering allows more of the carbohydrate you consume to contribute toward maximizing glycogen availability.

Is Carb Loading Just Eating Pasta The Night Before?

No.

This is probably one of the biggest carb loading misconceptions.

One large pasta dinner can provide a lot of carbohydrate, but it is unlikely to provide enough carbohydrate by itself to maximize glycogen stores.

For many athletes, an effective carb load may require several hundred grams of carbohydrates each day.

Trying to consume all of that at dinner would be extremely uncomfortable.

Instead, spread carbohydrate throughout the day.

For example:

Breakfast.

Morning snack.

Lunch.

Afternoon snack.

Dinner.

Evening snack.

Carbohydrate containing drinks can also help.

Why Carb Loading Can Feel Like So Much Food

Consider our 160 pound athlete with a target of approximately 725 to 870 grams of carbohydrate.

Carbohydrate contains approximately four calories per gram.

That means 800 grams of carbohydrates provides roughly 3,200 calories from carbohydrate alone.

Trying to obtain all of that from bulky whole foods can be difficult.

This is why athletes often adjust the composition of their diet during carb loading.

They may temporarily choose more carbohydrate dense foods and reduce foods that create excessive fullness.

The goal is not necessarily to eat dramatically more food volume.

The goal is to increase the percentage of your intake coming from carbohydrates.

Foods That Can Make Carb Loading Easier

There is no single perfect carb loading food.

Choose foods you tolerate well and have used before training.

Practical carbohydrate sources can include:

Rice.

Pasta.

Bread.

Bagels.

Cereal.

Oatmeal.

Potatoes.

Pretzels.

Fruit.

Bananas.

Applesauce.

Rice cakes.

Pancakes.

Juice.

Sports drinks.

Carbohydrate drink mixes.

Low fiber carbohydrate snacks.

The best foods are generally the ones that allow you to reach your carbohydrate target without creating excessive gastrointestinal discomfort.

Liquid Carbohydrates Can Be Useful

One of the easiest ways to increase carbohydrate intake without eating another large meal is to drink some of your carbohydrates.

This is especially useful when carbohydrate targets become very high.

For example, adding 60 grams of carbohydrate from a drink between meals may be considerably easier than adding another plate of food.

Our GlycoFuel carbohydrate formula can be used alongside normal foods as a convenient way to increase carbohydrate intake when your carb loading requirements become difficult to meet through meals alone.

Liquid carbohydrates should complement a well planned diet rather than automatically replacing your normal meals.

Should You Reduce Fiber During Carb Loading?

Potentially.

High fiber foods are healthy and should normally be part of a balanced diet.

However, temporarily reducing fiber intake immediately before a race may make aggressive carbohydrate loading easier for some athletes.

Fiber increases food volume and can contribute to fullness.

It can also increase stool volume and gastrointestinal activity.

Athletes who are prone to gastrointestinal problems during races sometimes favor lower fiber carbohydrate sources during the final day or two before competition.

This does not mean fiber is bad.

It simply means race nutrition has a different short term goal than everyday nutrition.

What About Fat?

Fat is also an important part of a healthy diet.

During an aggressive carb load, however, very high fat foods can make hitting carbohydrate targets more difficult because they provide substantial calories without contributing carbohydrates.

You do not need to eliminate fat.

Simply avoid allowing high fat foods to displace the carbohydrates you are intentionally trying to increase.

Should You Increase Protein?

You generally do not need to dramatically increase protein during carb loading.

Maintain your normal protein intake while allowing carbohydrate to become the dominant macronutrient during the loading period.

For example, instead of doubling the amount of meat at dinner, increase rice, pasta, bread, potatoes, or another carbohydrate source.

How Many Carbs Should You Eat The Morning Of A Race?

Carbohydrate intake does not stop when carb loading ends.

Pre-exercise recommendations generally fall in the range of approximately:

1 to 4 grams of carbohydrate per kilogram of body weight

during the:

1 to 4 hours before exercise.

The longer you have before the race, the larger the meal can generally be.

For example, a runner eating four hours before a marathon may tolerate a larger carbohydrate meal than someone eating only 60 minutes before the start.

For our 160 pound runner, who weighs about 73 kilograms, this could theoretically range from approximately 73 to 290 grams of carbohydrate depending on timing and individual tolerance.

You do not need to force the maximum amount.

Choose a meal that you have practiced during training.

Example Carb Loading Plan For A 160 Pound Runner

Suppose our athlete is running a marathon and wants to consume approximately 800 grams of carbohydrate during the day before the race.

A simplified day might look something like this:

Breakfast: 150 grams

Morning snack: 100 grams

Lunch: 175 grams

Afternoon snack: 100 grams

Dinner: 175 grams

Evening snack: 100 grams

Total:

800 grams of carbohydrate

Those numbers are only an example.

You could distribute the carbohydrates differently depending on appetite, schedule, food preferences, and gastrointestinal tolerance.

Should Trail Runners Carb Load?

Yes, if the race is sufficiently long.

Trail races are often particularly dependent on carbohydrate availability because they can last many hours.

A 50K might take one runner four hours and another runner eight hours.

Both are exercising far longer than the duration at which glycogen availability becomes important.

Trail runners should also remember that carbohydrate loading is only one piece of the nutrition strategy.

You still need a plan for consuming carbohydrates during the race.

Starting with high glycogen stores does not eliminate the need to fuel while running.

What About Ultramarathons?

Carbohydrate loading can be appropriate before ultramarathons as well.

The fact that an ultra may be performed at a lower average intensity than a marathon does not mean carbohydrate becomes irrelevant.

Ultrarunners still use carbohydrate during climbing, running, surges, and other higher intensity portions of the race.

The extreme duration of an ultramarathon makes your during race fueling strategy particularly important.

Carb loading simply allows you to begin the race with high carbohydrate availability.

Carb Loading Does Not Replace Race Fueling

This is important.

Muscle glycogen storage is limited.

Even after an effective carb load, you cannot store enough carbohydrate to fuel an entire marathon or ultramarathon without consuming additional carbohydrate.

During prolonged endurance exercise, athletes commonly benefit from consuming carbohydrates throughout the event.

The appropriate amount depends on exercise duration, intensity, gastrointestinal tolerance, and how well the athlete has practiced consuming carbohydrate during exercise.

Think of carb loading and race fueling as two parts of the same strategy.

Carb loading fills the tank before you start.

Race fueling helps keep carbohydrate coming in while you compete.

Train Your Gut Before Race Day

If you normally eat 300 grams of carbohydrate per day, suddenly attempting to eat 800 grams the day before your most important race may not go well.

Practice your carb load.

Use a long training weekend or lower priority race to test:

How much carbohydrate you can comfortably eat.

Which foods digest best.

How much fiber you tolerate.

Whether liquid carbohydrate helps.

How your pre-race breakfast feels.

Your bowel habits.

How you feel during the event.

Race nutrition should be trained just like pacing, shoes, and equipment.

Will Carb Loading Make You Gain Weight?

Possibly, temporarily.

Glycogen is stored with water.

As your muscles store additional glycogen, they also retain additional water.

That means the number on the scale may increase during carbohydrate loading.

For an endurance athlete about to race, this is generally not something to panic about.

The goal is to begin the event with high glycogen availability and adequate hydration, not to achieve the lowest possible body weight on race morning.

Common Carb Loading Mistakes

One of the biggest mistakes is waiting until dinner the night before the race.

Another is simply eating more of everything instead of specifically increasing carbohydrate.

Athletes also commonly make the mistake of eating unusually rich foods, excessive fiber, or unfamiliar meals because they are traveling or celebrating before a race.

Perhaps the most important mistake is never practicing the strategy.

Your biggest race should not be your first attempt at aggressive carbohydrate loading.

Use Our Free Carb Loading Calculator

Instead of guessing, use our free Carb Loading Calculator.

Enter your:

Body weight.

Expected race duration.

Loading window.

Number of meals and snacks.

Race morning meal timing.

Carbohydrate tolerance.

The calculator will estimate:

Your daily carbohydrate target.

Grams of carbohydrate per kilogram.

Total carbohydrates for the loading period.

Carbohydrates per meal or snack.

Race morning carbohydrate target.

This gives you a practical starting point that you can then refine during training.

Frequently Asked Questions

How many carbs should I eat when carb loading?

For prolonged endurance competition, approximately 10 to 12 grams of carbohydrate per kilogram of body weight per day for 36 to 48 hours is commonly recommended.

How many carbs should I eat before a marathon?

A marathon runner may benefit from approximately 10 to 12 grams of carbohydrate per kilogram per day during the final 36 to 48 hours before the race, followed by an appropriate pre-race carbohydrate meal.

When should I start carb loading for a marathon?

A modern carb loading strategy can generally begin around 36 to 48 hours before the race while training volume is reduced.

Do I need to carb load for a half marathon?

It depends on how long you expect the race to take. Aggressive carbohydrate loading becomes more relevant when exercise lasts longer than approximately 90 minutes.

Can I carb load with drinks?

Carbohydrate containing drinks can be a convenient way to supplement food during a carb load, particularly when very high carbohydrate targets make food volume uncomfortable.

Should I carb load before a 5K?

Most runners do not need an aggressive 36 to 48 hour carbohydrate load before an event lasting well under 90 minutes.

Should I carb load before an ultramarathon?

Carb loading can help maximize glycogen before an ultramarathon, but you will still need to consume carbohydrates during the race because stored glycogen is limited.

Is pasta good for carb loading?

Pasta can be an excellent carbohydrate source, but effective carb loading involves your overall carbohydrate intake across roughly 36 to 48 hours, not simply one large pasta dinner.

References

• Burke LM, Millet G, Tarnopolsky MA. Nutrition for distance events. Journal of Sports Sciences. 2007.
• Burke LM. Nutrition strategies for the marathon: fuel for training and racing. Sports Medicine. 2007.
• Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics. 2016.
• Wallis GA, Podlogar T. Dietary Carbohydrate and the Endurance Athlete: Contemporary Perspectives. Sports Science Exchange. 2022.
• Hargreaves M, Hawley JA, Jeukendrup A. Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance. Journal of Sports Sciences. 2004.