How long do milk and yoghurt last once opened?

Milk and yoghurt cause more fridge-door hesitation than anything else. The date has not passed but the smell has changed; or the date has passed and everything seems fine. In both cases the deciding factor is not the date — it is whether the pack has been opened.

The short answer

Product	Unopened	Once opened (fridge)
Pasteurised milk	Until the date on the pack	5–7 days
UHT (long-life) milk	Months at room temperature	5–7 days
Yoghurt	Until the date on the pack	7–14 days
Kefir, drinking yoghurt	Until the date on the pack	~10 days
Strained / Greek yoghurt	Until the date on the pack	~14 days

The most misunderstood line here is UHT milk. Because the carton sits on a shelf for months, people assume it stays robust after opening — it does not.

Why opened UHT milk is just ordinary milk

UHT milk is heated very briefly to a very high temperature and filled into a sterile carton. There are no bacteria inside; that, not any preservative, is where its shelf life comes from.

The moment you open it, that sterility is gone: bacteria from the air and the spout get in. From then on it is a normal milk with 5–7 days in the fridge. The same logic applies to many of the products we covered in how long do opened products last.

Practical consequence: if you cannot get through a litre in a week, a smaller carton wastes less than a large one.

The liquid on top of yoghurt is not spoilage

That clear liquid pooling on the surface is whey, and it is entirely normal. As yoghurt sits, its gel structure tightens and pushes liquid out — a process called syneresis. Stir it back in; it is the protein-rich part.

Spoilage looks different:

• Pink, orange or fuzzy mould — discard the whole pot. Scooping out the mouldy part is not enough, because yoghurt is soft and mould threads travel through it.
• A bulging lid or fizz — unwanted fermentation.
• A sharp, yeasty or bitter taste — beyond the normal tang.

We explain why cheese and yoghurt are treated differently in is mouldy cheese safe.

Soured milk: spoiled, or just sour?

When pasteurised milk sours, the bacteria doing it are usually lactic acid bacteria, which are not pathogens. That is why baking with slightly soured milk — pancakes, cakes, scones — is a long-standing practice, and the oven temperature moves it further onto the safe side.

Two cases where this does not apply:

• Raw, unpasteurised milk. Souring says nothing about whether pathogens are present.
• Milk that smells "dirty" rather than sour. Mould, bitterness or a colour change is not something baking rescues.

Once milk has been boiled, a new clock starts: cooled and refrigerated, it still needs using within a few days.

Where it should sit in the fridge

Milk and yoghurt belong on an inside shelf, not the door. The door is where the temperature swings most, which makes it the worst spot for the most sensitive things in the fridge. As the FDA points out, a fridge should be held below 4 °C (40 °F) — and only a thermometer can tell you that, not the numbers on the dial.

Keep milk in its own carton. Decanting it into a jug loses the date and adds a new source of contamination.

Does freezing help?

Milk freezes, but the texture changes: it looks grainy once thawed and is not pleasant to drink. It works fine in cooking and baking. Do not freeze a full container — milk expands as it freezes.

Frozen yoghurt loses its consistency badly and is not much use outside a smoothie.

To check how long a specific food keeps in the fridge, pantry or freezer, our shelf life lookup puts the three figures side by side.

In short

With milk and yoghurt, watch the day you opened it rather than the date. Unopened, it is fine until the date printed on the pack; once opened, a new window starts — 5–7 days for milk, 7–14 for yoghurt.

Remembering that "day I opened it" is the hard part. freshIt adds your items automatically from your grocery receipt and updates the date itself when you mark something as opened. See how it works on the features page.