How long do bananas last before they go bad?

The short version: a banana bought slightly green usually reaches full, speckled ripeness within two to five days on the counter, and stays genuinely good to eat for a couple of days past that before it tips into overripe. Putting it in the fridge does not stop this process the way refrigeration stops most fruit from turning — it just splits the story in two, so the peel and the fruit inside end up telling you different things.

Why a banana keeps changing after you buy it

Bananas are picked and shipped green on purpose, then ripened off the plant, which is why the one in the shop rarely matches the one on your counter three days later. The fruit does this to itself: a ripening banana produces ethylene gas, which triggers its own starch to convert into sugar and softens the cell walls from the inside out. That is the entire flavour story — a green banana is starchy and firm because the conversion has not happened yet, and a spotted one is sweet and soft because it mostly has.

Ethylene is also why a whole bunch ripens together, and faster than a single banana would on its own — each fruit is gassing its neighbours, concentrated most heavily right at the stem cluster where they all touch. It is why a banana ripens noticeably faster next to apples or a hard avocado, and why the advice to keep produce apart or push it together depending on what you want is not folklore; it is the same gas doing opposite jobs depending on your goal.

What the fridge actually does — and does not do

Cold does slow the enzymes doing the ripening inside a banana. What it does not do is protect the peel, which is thin and reacts to cold by producing dark pigments almost immediately — often within a day. The result looks alarming and means very little: a banana can go fully black on the outside within a day or two of refrigeration while the fruit underneath stays pale, firm and perfectly fine, sometimes for several more days than it would have lasted on the counter. This is close to the opposite problem a raw sweet potato has in the cold, where the damage is real and happens to the flesh itself. Here the ugliness is almost entirely cosmetic, on the one part of the banana nobody eats.

Timing matters, though. Refrigerating a banana that is still green does not preserve it in that state for later — it mostly just stalls the ripening enzymes without finishing the job, and a banana chilled too early sometimes never develops full flavour once it warms back up. The fridge is a good tool for pausing a banana once you are happy with how ripe it is, not a way to bank a green one for next week.

Slowing it down or speeding it up on purpose

Split the bunch up. A single banana away from the others ripens noticeably slower than one still bundled at the stem, simply because it is breathing in less of everyone else's ethylene.
Wrap the stem tightly in cling film. This is the one genuinely effective trick: it traps the gas right at the point it concentrates most instead of letting it reach the whole bunch, and can buy a day or two.
Keep it away from apples and avocados if you want it to last — or right next to them if you are trying to ripen a hard avocado for tonight. Same gas, opposite use.
Once it is as ripe as you want, the fridge buys real time. The blackened peel is the cost of that extra time, not a sign anything is wrong with what is inside it.

What to do with one that has gone past eating out of hand

A banana that has turned fully brown-spotted or soft is not a failure — for baking, it is often the best stage there is, because the starch-to-sugar conversion is essentially finished for you. This is the point most banana bread recipes are actually written for. If you are not baking today, the fruit freezes well: peel it first, because a frozen peel is a genuine hassle to get off, then freeze whole or sliced. Frozen banana is for blending and baking rather than eating thawed as-is — the texture changes once the water inside it turns to ice and back — but for a smoothie or a loaf it works exactly as well as fresh, for months.

What actual spoilage looks like

Skin fully black, fruit inside still firm and pale. Overripe, not spoiled — this is a quality and flavour stage, not a safety one, and often the best banana for cooking with.
A small soft, dark bruise under otherwise firm peel. Localised damage from a knock in transit. Trim it and use the rest.
Very soft throughout, leaking, or a sour, almost alcoholic smell rather than the sweet smell of a ripe one. This is genuine fermentation, past the point of being worth eating.
Visible fuzzy mould, usually starting at the stem end. The point to stop, not trim around.

The practical problem with bananas is rarely knowing any of this — it is that a bunch bought on Monday quietly turns into Thursday's ignored, blackened problem because nothing marked how long it had actually been sitting there. Munch logs an item against the day it was added and groups recipes so the ones that use up your oldest ingredients surface first, which is exactly the nudge a darkening bunch of bananas needs to become tonight's banana bread instead of tomorrow's bin.

None of this needs a rule for every stage. It needs one distinction: a black peel is a report on time passed, not a verdict on what is inside. Judge the fruit, not the skin, and a banana keeps being useful for days longer than most people give it credit for.