A medium banana (about 7 to 8 inches long) contains roughly 27 grams of total carbohydrates. That includes 3 grams of fiber and about 15 grams of naturally occurring sugar, with the rest coming from starch. The exact count shifts depending on the banana’s size and how ripe it is.
Carbs by Banana Size
Bananas vary quite a bit in size, and so does their carb content. A medium banana weighing around 118 grams is the standard reference, but here’s how the numbers scale:
- Extra small (6 inches, ~81g): 19 grams of carbs
- Small (6–7 inches, ~101g): 23 grams of carbs
- Medium (7–8 inches, ~118g): 27 grams of carbs
- Large (8–9 inches, ~136g): 31 grams of carbs
Most bananas you’ll find at a grocery store fall in the medium to large range. If you’re eyeballing it, the difference between a small and large banana is about 8 grams of carbs, roughly the equivalent of two teaspoons of sugar.
Fiber and Net Carbs
A medium banana provides about 3.1 grams of fiber. Since fiber passes through the body without being digested or raising blood sugar, many people subtract it to get a “net carb” count. For a medium banana, that comes to roughly 24 grams of net carbs.
That fiber is a mix of soluble and insoluble types. The soluble fiber helps slow digestion, which is one reason bananas don’t spike blood sugar as sharply as you might expect from a fruit with 15 grams of sugar.
How Ripeness Changes the Carb Profile
The total carbs in a banana stay about the same whether it’s green or spotted brown. What changes dramatically is the type of carbohydrate inside. A green banana is mostly starch, with up to 76% of its dry weight as starch (about a third of that being resistant starch, a type your body can’t fully digest). As the banana ripens, enzymes break that starch down into simple sugars. By the time it’s fully ripe with brown spots, starch content drops to around 25%.
This is why a ripe banana tastes so much sweeter than a green one, even though you’re eating the same amount of total carbohydrate. In a fully ripe banana, sucrose makes up the largest share of sugar, followed by smaller amounts of fructose and glucose. A green banana, by contrast, has almost no free sugar at all.
This matters practically. If you’re trying to manage blood sugar, a slightly underripe banana (still firm, pale yellow) will have a slower, more gradual effect than a soft, spotted one. The glycemic index of bananas ranges from about 42 to 62 depending on ripeness, placing them in the low to medium range.
Green Bananas and Resistant Starch
Green bananas are one of the richest natural sources of resistant starch, a carbohydrate that behaves more like fiber than sugar. It resists digestion in the small intestine and instead feeds beneficial bacteria in the gut. A study using unripe banana flour found that consuming about 8 grams of the flour (containing roughly 5 grams of resistant starch) led to lower fasting insulin levels over six weeks and improved insulin sensitivity compared to a control group.
As a banana ripens, resistant starch drops sharply. Most of it converts during the transition from green to yellow, so once a banana is fully yellow, it retains only a fraction of its original resistant starch. If you specifically want resistant starch, eat your bananas when they’re still a bit green and firm.
How Bananas Fit Low-Carb Diets
For a standard diet, a banana’s 27 grams of carbs is moderate. It’s comparable to a slice and a half of bread or a small serving of rice. Most people eating a balanced diet can include one or two bananas a day without concern.
For strict low-carb or ketogenic diets, bananas are one of the trickier fruits. A ketogenic diet typically limits total carbs to around 20 to 50 grams per day. A single medium banana uses up more than half of a 50-gram daily limit, or nearly all of a 20-gram one. Per 100 grams, bananas contain about 20 grams of net carbs, which is significantly higher than berries (5 to 7 grams per 100 grams) or cantaloupe (about 7 grams per 100 grams). If you’re on keto and want banana flavor, half of a small banana is a more realistic portion.
For people managing diabetes or prediabetes, bananas aren’t off the table. Pairing a banana with protein or fat (peanut butter, yogurt, nuts) slows the sugar absorption and flattens the blood sugar response. Choosing a less ripe banana helps further.
What Else You Get With Those Carbs
A medium banana delivers about 110 calories along with 450 milligrams of potassium, which is roughly 10% of most adults’ daily needs. It also provides small amounts of vitamin B6 and vitamin C. The combination of fast-acting sugar, slower-digesting starch, and potassium is why bananas are popular before and after exercise. They’re effective at replenishing glycogen stores and replacing electrolytes lost through sweat.
Compared to other common fruits, bananas are on the higher end for carbs. An apple of similar weight has about 19 grams of net carbs, while a cup of strawberries has around 8 grams. But bananas are also more calorie-dense and more portable, which makes them a practical snack when you need sustained energy rather than a quick sugar hit.