From the YummyYucky team, founded by Nancy Nash
How long is prepared formula good for?
Every formula parent has stood in the kitchen at 3am holding a half-finished bottle, doing math. Here is the math, done once, from the CDC's rules: 2 hours for a fresh bottle at room temperature, 1 hour once a feeding starts, 24 hours in the fridge for an untouched bottle. The rest of this page is the details and the why.
These time limits are food-safety rules, not suggestions. When in doubt, throw it out: a poured ounce of formula costs pennies, and the rules exist because bacteria in milk are invisible, tasteless, and fast. Follow your formula label if it is stricter, and ask your pediatrician about anything specific to your baby.
Freshly mixed, at room temperature: 2 hours
A bottle prepared from powder or concentrate is good for 2 hours from preparation if nobody has drunk from it. Room-temperature formula is a warm, sugary, protein-rich liquid, which is also the exact recipe bacteria would order for themselves. Two hours is the window before growth takes off.
In the fridge, untouched: 24 hours
If a freshly mixed bottle will not be used within 2 hours, refrigerate it immediately and use it within 24 hours. This is how you batch: mix the night's bottles, straight into the fridge, warm as needed. The rule only holds for bottles that were never fed from.
Once a feeding starts: 1 hour, then toss it
The moment your baby starts drinking, the bottle has 1 hour. After that, whatever is left gets thrown out, not refrigerated, not saved for the next waking. This is the rule that feels the most wasteful and matters the most, and it is bacteria, not superstition: drinking backwashes saliva into the milk, seeding it with bacteria that keep multiplying even in the fridge. A saved half-bottle is a culture experiment with a cute label.
Warmed bottles: the clock never restarts
Warming counts against the same limits, never resets them. Warm a bottle under running warm water or standing in a bowl of warm water, never in the microwave (it heats unevenly and can scald a baby's mouth). A warmed bottle should be used for that feeding, and a warmed, partly finished bottle never goes back in the fridge.
Opened ready-to-feed: 48 hours in the fridge
An opened container of ready-to-feed formula should be covered, refrigerated, and used within 48 hours. Once you pour it into a bottle, the same 2-hour and 1-hour rules apply as for mixed formula. Some labels give a shorter window; the label wins when it is stricter.
Opened powder: 1 month
A container of powdered formula should be used within 1 month of opening. Keep it cool and dry with the lid tight, not in the fridge. Write the date on the lid when you crack it; a can opened "at some point during the blur" is not a date.
A quick word on water
Mix powder with safe drinking water; if you are unsure about your tap water, ask your pediatrician or local health department. Powdered formula is not sterile, and for the highest-risk babies (younger than 2 months, born premature, or immunocompromised) the extra-cautious options are ready-to-feed formula, or mixing powder with water heated to at least 158 F (70 C) and then cooling the bottle to body temperature before feeding. The germ in question, Cronobacter, is rare but serious in young infants, which is why the fuss exists.
Let the timestamps do the remembering
Every rule on this page is really a question about when something happened, and 3am you is a terrible witness. Log each bottle in YummyYucky and the timestamps do the remembering: when it was made, when the feed started, and whether that bottle on the counter is 40 minutes old or from the before times.
No account needed to start: tap what was in it and how much, and today’s total adds itself up.
Log a bottle in ten seconds →Related reading
See how much formula babies need, the by-age guides at 2 months, 4 months, and 6 months, and how to store breast milk, which has its own, different rules.
This is general information, not medical advice. Storage guidance can change and labels vary, so follow your formula's label when it is stricter, and talk to your pediatrician about safe preparation for your baby, especially for newborns, premature babies, or babies with immune concerns. In an emergency, contact emergency services.
Frequently asked questions
Can I put a bottle back in the fridge after my baby drank some of it?
No. Once a feeding starts, use the bottle within 1 hour and throw out whatever is left. Drinking from the bottle backwashes saliva into the milk, and formula is an excellent place for those bacteria to grow, even in the fridge. This is the most commonly broken rule and the one most worth keeping.
How long can a prepared bottle of formula sit out?
Use a freshly prepared bottle within 2 hours, and within 1 hour of the moment your baby starts drinking from it. If a fresh, untouched bottle will not be used within 2 hours, put it in the fridge right away and use it within 24 hours.
Can I make bottles ahead for the day or for nighttime?
Yes, as long as they go straight into the fridge. Mix a bottle (or a batch), refrigerate it immediately without feeding from it, and use it within 24 hours. This is the legal version of the 3am shortcut: the fridge bottle just needs warming, and nobody is scooping powder half asleep.
How long is ready-to-feed formula good after opening?
Once opened, cover the container, refrigerate it, and use it within 48 hours. The 2-hour and 1-hour rules still apply to whatever you pour into a bottle. Check your label too: if the manufacturer gives a shorter window, follow the shorter one.
Does warming a bottle restart the clock?
No, warming only ever shortens the runway. A warmed bottle should be used for that feeding: once your baby starts it, the 1-hour rule applies, and a warmed bottle should never go back in the fridge for later. Warm bottles under running warm water or in a bowl of warm water, and never in the microwave, which heats unevenly and can scald.
How long does powdered formula last after opening the can?
Use an opened container of powdered formula within 1 month. Keep it in a cool, dry place with the lid tight, not in the fridge, and write the date you opened it on the lid so future 3am you does not have to do archaeology.
Sources
- CDC: Infant Formula Preparation and Storage
- FDA: Handling Infant Formula Safely: What You Need to Know
- CDC: Protect Your Baby from Cronobacter (prevention infographic)
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Start tracking for freeLast updated September 2026. Next review December 2026. How we write these: built from current published guidance from the AAP, CDC, FDA/EPA, NIAID, WHO, and other pediatric and public-health authorities, with sources cited on the page. See our editorial and medical policy for how we research, source, and update these, and how we double-check the food advice.
This is general information, not medical advice, and is not individualized for your baby. Always talk to your pediatrician about your baby's diet, introducing allergens, and any reaction. In an emergency, contact emergency services.
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