A medium banana (about 118 grams) contains 27 grams of total carbohydrates and 14 grams of sugar. The remaining carbs come from 3 grams of fiber and roughly 10 grams of starch, though that starch-to-sugar ratio shifts dramatically depending on how ripe the banana is.
Full Carb Breakdown by Size
Bananas vary quite a bit in size, and so does their carb count. A medium banana, the standard reference used on nutrition labels, weighs about 118 grams (just over 4 ounces). Here’s what it contains:
- Total carbohydrates: 27 g
- Total sugars: 14 g
- Dietary fiber: 3 g
A small banana (about 100 grams) lands closer to 23 grams of carbs and 12 grams of sugar. A large banana, the kind that’s noticeably longer than your hand, can reach 31 to 35 grams of carbs. If you’re tracking carbs for blood sugar management, weighing your banana once or twice gives you a much better estimate than eyeballing it.
How Ripeness Changes the Sugar Content
This is the part most people don’t realize: the same banana can have wildly different sugar levels depending on when you eat it. A green, unripe banana is mostly starch, with only about 3.2 grams of sugar per 100 grams of fruit. A ripe yellow banana contains 12 to 13 grams of sugar per 100 grams. The total carbohydrate count stays roughly the same, but the type of carb shifts as the banana sits on your counter.
Here’s what’s happening inside the peel. An unripe banana stores about 21 grams of starch per 100 grams of fruit. Much of this is resistant starch, a type your body can’t fully digest, so it behaves more like fiber than like sugar. As the banana ripens, enzymes break that starch down into glucose and fructose (in roughly equal amounts). By the time it’s fully ripe with brown spots, the starch drops to about 1 gram per 100 grams. The fiber content drops too, from around 18 grams per 100 grams in unripe fruit to about 2 grams in overripe bananas.
Once a banana reaches the ripe stage, though, the sugar content plateaus. An overripe banana with lots of brown spots has about the same amount of sugar as a perfectly yellow one. It just tastes sweeter because the texture softens and the acids break down.
What This Means for Blood Sugar
Despite having 14 grams of sugar, a ripe banana has a glycemic index of 51, which falls in the low category (under 55). A slightly underripe banana scores even lower at 42. The glycemic load, which accounts for actual portion size, is moderate at 13 for a ripe banana and 11 for a less ripe one. For context, a glycemic load under 10 is considered low, and above 20 is high.
The fiber, resistant starch, and overall structure of the fruit slow down how quickly those sugars hit your bloodstream. This is why eating a banana feels different from drinking a glass of juice with the same amount of sugar. If you’re managing blood sugar and want to minimize the spike, choosing bananas that are still slightly firm and yellow (not spotted) gives you more resistant starch and a lower glycemic response.
How Bananas Compare to Other Fruits
Bananas have a reputation for being high in sugar, but they’re actually moderate compared to other popular fruits. One medium banana has about 15 grams of sugar. A large apple has 25 grams. A large orange has about 17 grams. Grapes and mangoes are also higher in sugar per typical serving.
Where bananas do stand out is in total carbohydrates, because of their starch content. An apple and a banana might weigh about the same, but the banana packs more total carbs since it carries starch on top of its sugars. This makes bananas denser in carbs per bite, which is useful if you want quick energy before a workout and worth knowing if you’re counting carbs closely.
Net Carbs in a Banana
If you follow a low-carb or keto approach, you probably think in terms of net carbs (total carbs minus fiber). For a medium ripe banana, that’s 27 minus 3, giving you 24 grams of net carbs. That’s high enough to use up most or all of a typical daily keto carb budget of 20 to 50 grams.
For a greener banana, the math gets more favorable. The higher resistant starch content means fewer of those carbs are actually absorbed, though nutrition labels don’t always reflect this. Some people subtract resistant starch alongside fiber, which would bring the effective carb count of a green banana down further, but there’s no standardized way to measure this at home. The practical takeaway: if you’re on a very low-carb diet, bananas are one of the harder fruits to fit in. If you’re simply watching your carb intake without strict limits, a small or medium banana is a reasonable choice that delivers potassium, vitamin B6, and fiber alongside its carbs.