How to Calculate Net Carbs

“Net carbs” isn’t a scientific term or regulated method. It’s something generated by low-carb diet enthusiasts to help you keep track of carbohydrates that raise your blood sugar. Proponents of such diets claim that elevated blood sugar levels are the culprits for weight gain, although these statements haven’t been scientifically proved yet. Calculating your net carbs requires just basic math skills -- a little subtraction and balancing.

Determine the Portion Size

Nutrition information is based on one serving. Before correctly calculating your net carb intake, know the proper portion size. Just because a package is small and seems like it might be one serving doesn’t mean it is. The serving size is located just below “nutrition facts” on the back panel. You’ll see both the serving size in common measurements -- like cups and ounces -- and in grams, as well as the number of servings per container. So if the serving size is 1 cup and there are two servings in the package, you know one serving is half a cup..

Locate the Total Carbohydrates

About halfway down the label, you’ll see “total carbohydrate” listed in bold lettering. This number includes all types of carbohydrates. Sugar, starch, fiber and sugar alcohol grams all make up the total carbohydrates, since they all have a similar chemical makeup. Some manufacturers may include the specific sugar and starch grams below the total carbohydrates, but this isn’t a required standard in food labeling.

Subtract the Fiber

Once you know the total carbohydrates per serving, subtract the fiber carbs. The reasoning behind this is that fiber doesn’t metabolize into glucose, the simple sugar transformed from sugar and starch that brings your blood sugar up. Fiber travels through your digestive tract without going through that glucose-conversion process. This is why some diets allow you to subtract fiber grams from the total carb grams -- in some cases only if fiber amounts to 5 grams or more, though. For instance, if a serving of whole-grain pasta has 30 grams of total carbohydrates and 5 grams of fiber, you’ll have only 25 grams of net carbs: 30 - 5 = 25.

Subtract the Sugar Alcohols

Sugar alcohols, like sorbitol, malitol, lactitol or sucralose, aren't completely carb- and calorie-free. Usually starch and sugar carbohydrates have 4 calories per gram. While everyone digests sugar alcohols differently, it's estimated that they have an average of 2 calories per gram, unless otherwise listed. So because you're typically getting roughly half of the glucose-elevating carbohydrate, subtract half of the sugar alcohols. As an example, if a food has 4 grams of sugar alcohols -- they'll be listed under "total carbohydrates" -- subtract 2 grams from the total carbs to get your net carbs.

Keep Track of Your Daily Allowance

Keep tabs on your daily net carb intake. Certain diets allow you to have as much as 100 grams of net carbs each day. Others have you limit yourself to less than 20 grams, however. Ideally, you should split up your net carbs evenly among meals -- leave some out for snacks, too. If the stage of your plan allows you to have 50 grams of net carbs per day and you get 25 grams from that one serving of pasta, you’re only left with another 25 grams for the rest of the day. Choose wisely and spread them out more evenly so that you don’t go overboard or deprive yourself at any particular meal.