A medium banana contains about 14 grams of sugar. That number shifts depending on the size of the fruit and, more importantly, how ripe it is. A small banana (six to seven inches) has closer to 12 grams, while a large one (eight to nine inches) can reach 17 grams or more.
Sugar Content by Banana Size
Bananas come in a wider size range than most people realize, and that directly affects sugar content. Per 100 grams of ripe banana flesh, there are roughly 12.2 grams of sugar. Since a small banana weighs about 100 grams of edible fruit and a large one closer to 135 grams, the difference between sizes adds up quickly. If you’re tracking carbohydrate intake, weighing the peeled fruit gives you a more accurate count than estimating by length.
Types of Sugar in a Banana
Not all fruit sugar is the same, and bananas have a distinctive mix. Per 100 grams of ripe fruit, about 7.9 grams come from sucrose (table sugar), 3.9 grams from glucose, and 3.8 grams from fructose. That makes bananas unusually high in sucrose compared to many other fruits, which tend to lean more heavily on fructose. Your body breaks sucrose down into equal parts glucose and fructose during digestion, so the practical difference is small, but the ratio helps explain why bananas taste distinctly sweet rather than having the sharper sweetness of, say, an apple.
How Ripeness Changes the Sugar Content
This is the part most people don’t expect: a green banana and a spotted brown banana contain roughly the same total carbohydrates, but the form of those carbohydrates is dramatically different. An unripe banana stores about 21 grams of starch per 100 grams. As the fruit ripens, enzymes break that starch down into sugars. By the time a banana is fully ripe, its starch content drops to about 1 gram per 100 grams. That’s a near-complete conversion.
The shift happens in stages. Slightly ripe bananas (mostly yellow, firm) still hold around 4.5 grams of starch per 100 grams. Ripe bananas with a few spots drop to about 2.5 grams. Overripe bananas, the soft ones with heavy brown spotting, retain less than half a gram of starch. The sugar increase is front-loaded: there’s a large jump in fructose, glucose, and total sugar as a banana goes from green to ripe, but sugar levels don’t actually climb much further between ripe and overripe. The overripe banana just tastes sweeter because the remaining starch is nearly gone and the texture is softer.
This has a real practical takeaway. If you want a banana with less available sugar hitting your bloodstream quickly, choose one that’s still slightly firm and yellow. The resistant starch in a less-ripe banana acts more like fiber, passing through your upper digestive tract without being fully broken down.
How Bananas Affect Blood Sugar
Despite their sugar content, ripe bananas have a low glycemic index of 51, according to the International Glycemic Index Database. Slightly underripe bananas score even lower at 42. Both values fall in the “low GI” category (under 55), meaning they raise blood sugar more gradually than white bread, rice, or most processed snacks. Their glycemic load, which accounts for portion size, is moderate at 13 for ripe and 11 for underripe.
Part of the reason bananas don’t spike blood sugar as aggressively as their sugar content might suggest is fiber. A ripe banana contains about 0.6 grams of soluble fiber and 1.2 grams of insoluble fiber per 100 grams. Soluble fiber slows the rate at which sugar enters your bloodstream. Pairing a banana with a source of protein or fat, like nuts or yogurt, slows absorption further.
If you’re managing diabetes or prediabetes, bananas aren’t off-limits, but individual responses vary. Some people see a noticeable blood sugar rise from a banana while others barely register it. Choosing a smaller, firmer banana and eating it alongside protein or fat is a reliable way to blunt the glycemic effect.
How Bananas Compare to Other Fruits
Bananas sit on the higher end of the sugar spectrum for common fruits, but they’re not outliers. Per 100 grams, bananas contain 12.2 grams of sugar compared to 8.6 grams for oranges. Strawberries and watermelon come in lower (around 5 to 6 grams per 100 grams), while grapes and mangoes land higher. The comparison is slightly misleading, though, because you eat an entire banana in one sitting but might eat only 80 grams of mango. Portion size matters as much as sugar density.
Bananas also deliver potassium, vitamin B6, and magnesium alongside their sugar, which is part of why nutrition guidelines consistently categorize whole fruit, bananas included, differently from added sugars. The fiber, water content, and micronutrients change how your body processes the sugar compared to the same number of grams from a candy bar or soda.