Grams per day before the start

Carb Loading Calculator

How many carbs should you eat before a marathon? Enter your body weight and target to get grams per day for the loading window, split across meals and snacks.

Example values are filled in. Use a target you have practiced before a long run.

Expected finish time

hoursminutesseconds

Body weight

Carbohydrate target

The research range is 10 to 12 g per kg for events over 90 minutes and 7 to 12 g per kg the day before shorter ones.

Loading days

Meals and snacks per day

Carbohydrate per day

700g

Inside the 10 to 12 g per kg range the research describes for 36 to 48 hours before the start.

Each meal or snack: 117 g
Over 2 days: 1,400 g
Range for your finish time: 10 to 12 g per kg
Loading window: 36 to 48 hours before the start

Events over 90 minutes get the full loading window. Reduce training through these days so the stores stay full.

Take the plan into race week.

Vitadel Run schedules your taper and race week, and Ask Vitadel answers nutrition and race-day questions from your own training.

Get Vitadel Run

Free to download on iPhone and Apple Watch.

This is arithmetic on the target you enter. It does not account for medical conditions or dietary needs, and it does not plan fueling during the run. Practice the loading before a long run, not for the first time in race week.

Turn a target per kilogram into grams per meal

Carbohydrate loading fills your muscles’ glycogen before an event that lasts longer than about 90 minutes. The research gives the target per kilogram of body weight per day. This calculator multiplies it out for your weight, totals it over the loading window, and splits each day across meals and snacks.

Pick the target per kilogram

Burke and colleagues’ review and the 2016 joint position stand describe 10 to 12 g per kg per day for 36 to 48 hours before events over 90 minutes, and 7 to 12 g per kg in the day before shorter events. The calculator shows the range that fits your finish time. The target you enter is yours.

grams per day = body weight (kg) × grams per kg

Choose the loading window

Two days covers the 36 to 48 hours in the research. One day suits a shorter event or a first attempt. The total for the window is the daily amount times the days. Training drops during these days so the stores stay full.

Spread it across the day

Daily grams divided by your meals and snacks gives the size of each. Smaller, more frequent portions are easier to finish than three large meals, and lower-fiber choices sit better. Practice the loading before a long run, not for the first time in race week.

grams per meal = grams per day ÷ meals and snacks

Example: 70 kg, four-hour marathon, 10 g per kg

70 kg × 10 g gives 700 g of carbohydrate per day, 1,400 g over two days. Across six meals and snacks that is about 117 g each. At 8 g per kg the daily total drops to 560 g. Enter your weight and a target you have practiced.

Sources

Common questions

How many carbs should I eat before a marathon?

The research range for events over 90 minutes is 10 to 12 g per kg of body weight per day for 36 to 48 hours. For a 70 kg runner that is 700 to 840 g per day. Enter your weight to see yours, then use a target you have practiced before a long run.

Do I need to carb load for a half marathon?

If you expect to run longer than about 90 minutes, the loading guidance applies. If you will finish faster, the position stand describes 7 to 12 g per kg in the day before. The calculator switches ranges from the finish time you enter.

Do I need a depletion phase first?

No. Burke and colleagues note that trained runners reach high glycogen stores with 36 to 48 hours of high carbohydrate intake and reduced training, without a depletion phase beforehand.

Will I gain weight?

Often, a little. Glycogen is stored with water, so the scale can rise during loading. The extra is fuel and fluid you use on the course.

What should I eat?

The calculator counts grams, not foods. Choose carbohydrate-rich foods you digest well, read labels for the grams, and keep fiber and fat modest in the final 24 hours. Rehearse the plan before a long run.

Does this replace fueling during the race?

No. Loading fills your stores before the start. During the run you still need carbohydrate each hour, which the marathon fueling calculator plans from your finish time and gel size.

More free tools

All tools

Arrive at the start line ready.

Vitadel Run plans base, build, peak, and taper, adapts each session to your sleep, HRV, and recovery, and answers race-week questions from your own training data.