How Long Does a Made-Up Formula Bottle Last? (UK, NHS Rules)

Formula is one of the few bits of baby care where there is a right answer, written down. The NHS gives specific times for how long a made-up bottle keeps, and because the risk being managed is a nasty bacterial infection, the numbers are worth knowing exactly. This is a short page on purpose: the question is "how long?", and the answer is a short list.

The short answer: once formula is made up, the NHS says use it within 2 hours at room temperature, within 4 hours in a cool bag with an ice pack, or within 24 hours in the fridge. "Make up a fresh feed only when your baby needs it." Anything left in the bottle after a feed goes in the bin, not back in the fridge.

The NHS numbers at a glance

Those are the NHS formula milk: common questions figures, quoted. The NHS's preferred position is one further step back: "Make up a fresh feed only when your baby needs it." The stored-feed numbers are the fallback for when fresh isn't realistic, not a target.

Why these particular numbers

Powdered infant formula is not sterile. It can contain bacteria that don't matter in the tin, but can multiply once the powder is mixed with warm water. Two things keep that risk small: killing bacteria in the powder at the moment of mixing, and limiting the time afterwards.

Killing bacteria at mixing is why the NHS method uses hot water. In the NHS's own words: "Water at 70C or more will kill any harmful bacteria. Boil the water. Then leave the water to cool for no more than 30 minutes, so that it remains at a temperature of at least 70C." Then: "Always put the water in the bottle first, while it is still hot, before adding the powdered formula."

Limiting the time afterwards is what the fridge, cool bag and room-temperature numbers are about. The colder the storage, the slower bacteria grow — hence 24 hours in the fridge versus 2 hours on the kitchen counter.

How long does formula last once baby starts drinking it?

Once the teat touches the baby's mouth, bacteria from the mouth are in the bottle too. The NHS instruction is simple: "If there is any made-up formula left in the bottle after a feed, throw it away." Don't finish it later, don't offer it after a nap, and don't put a half-drunk bottle back in the fridge. The 24-hour fridge rule applies to made-up and not yet drunk from, not to leftovers.

Taking formula out of the house

Three NHS-approved options for a day out:

• Make up when needed. Take a flask of just-boiled water (hot enough to still be at least 70°C when you use it), a measured amount of powder in a separate clean container, and an empty sterile bottle. Mix at the point of feeding. This is the fresh-when-needed version, and it's the NHS's preferred approach.
• Cool bag with an ice pack. If you have made the feed up at home, cooled it under cold running water, and are travelling, keep the bottle in a cool bag with an ice pack and use it within 4 hours.
• No ice pack, no fridge. The NHS says the made-up feed "must be used within 2 hours." That's the same number as room temperature in your own kitchen — the clock doesn't care where the room is.

Ready-to-feed cartons are a reasonable backup for a day out: they're sterile until opened, so they don't need the 70°C step. Once opened, treat them the same as made-up powder: use quickly, bin any leftovers after a feed.

What about night feeds?

The gentle question behind this one is usually "can I make them up in advance and keep them in the fridge, so 2am is just reheat-and-feed?" The honest answer is that it's safer not to. A row of pre-made bottles in the fridge is 24 hours of risk management; a flask of just-boiled water, a measured pot of powder and a clean bottle is one feed's worth. The flask method is the NHS's shortcut for night feeds, and it holds up to tired hands.

If a prep machine or similar fits your household, the NHS's position is simple: "If you use a baby formula preparation machine, follow the manufacturer's instructions." It doesn't recommend or warn off any specific model.

Sterilising still matters

Separate from how long the milk lasts: the bottle it goes into has to be sterile. The NHS guidance is to sterilise all feeding equipment — bottles, teats, screw rings, caps and anything else that touches the feed — "until they're at least 12 months old." A sterile bottle plus hot-water mixing plus the time limits above is the three-layer safety net that keeps the number of infant formula infections low.

When to call someone

Rare, but worth knowing. If a baby who has had formula shows signs of being very unwell — persistent vomiting, bloody or very runny nappies, lethargy, a high temperature, or no wet nappies for several hours — don't guess. Call NHS 111, your GP, or 999 if they look seriously ill. Formula is overwhelmingly safe; it's worth being specific about the one thing that isn't.

Knowing when the bottle was made

The weak link in all of this is memory. "Was that bottle made at 10am or 11?" is harder to answer at 2am than it should be. Logging each feed with its time is the quiet fix — not for the sake of a chart, but so the question has an answer. CubTrack logs feeds, including which bottle and when it was made, on the free tier, and your partner sees the same list, so whoever is on the next feed doesn't have to ask.

Related reading

• Formula feeding guide: how much, how often, how to get it right
• How many baby bottles do I need?
• How much milk should a baby drink?
• Combination feeding: breast and bottle together
• Tracking feeds, sleep and nappies without the mental load

Frequently asked questions

How long can a made-up formula bottle sit out at room temperature?

The NHS says to use it within 2 hours at room temperature. After that, throw it away.

How long does made-up formula last in the fridge?

24 hours, as long as it was made with water at 70°C or more, cooled quickly, and hasn't been drunk from. Once a baby has started drinking it, don't put the rest in the fridge for later.

How long does made-up formula last in a cool bag?

4 hours in a cool bag with an ice pack. Without an ice pack or a fridge, the NHS says it must be used within 2 hours.

Can I make up formula in advance?

The NHS recommends making up a fresh feed only when your baby needs it, because that's the safest option. If making ahead is the only way the day works, the 24-hour fridge rule gives you a window — but prepping a flask of hot water and a measured pot of powder is a safer and often easier workaround for nights and days out.

Can I reheat a made-up bottle?

Yes, but once, and only before it has been drunk from. The NHS way is to warm it standing in a jug of warm water, with the bottle lid on; a bottle warmer is also fine. Microwaves aren't recommended because they heat unevenly. Test a few drops on the inside of your wrist before feeding.

What if my baby doesn't finish a bottle?

Throw the rest away. The NHS says: "If there is any made-up formula left in the bottle after a feed, throw it away." Don't save it for later or top it up with fresh milk.

Does formula go off if it looks fine?

It can. The point of the time limits isn't that the milk looks or smells bad — it's that bacteria you can't see or taste multiply over time. The clock, not the sniff test, is what you follow.

What about ready-to-feed cartons?

Unopened, they keep as the label says. Once opened, treat the same as made-up powder: use quickly, don't save leftovers after a feed, and discard what's left in the bottle at the end. If you decant into a bottle, use a sterile one.

Formula storage and preparation information quoted and summarised from the NHS in October 2026. This is general information, not medical advice; speak to your health visitor, GP or NHS 111 about your baby. CubTrack is made by OakFox Limited.