Prepared infant formula can be stored in the refrigerator for up to 24 hours. That’s the limit set by the CDC, and it applies to powdered formula that’s been mixed with water as well as ready-to-feed formula that’s been opened. Once that 24-hour window closes, any unused formula should be thrown out.
The 2-Hour and 24-Hour Rules
Two timelines matter when it comes to formula safety. The first is room temperature: once you mix a bottle of formula or open a container of ready-to-feed formula, you have about 2 hours before it needs to either be fed to your baby or moved into the fridge. Formula left at room temperature beyond that point should be discarded, not refrigerated.
The second timeline starts once the bottle goes into the fridge. From that point, you have 24 hours to use it. This applies whether you made one bottle or prepped several for the day ahead. If you’re batch-preparing bottles for nighttime feeds or daycare, label each one with the time it was made so you’re not guessing later.
Bottles Your Baby Has Already Started
A bottle your baby has partially finished is a different situation entirely, and the rules are stricter. Once a baby’s lips touch the nipple, saliva enters the formula, and that saliva introduces bacteria that multiply quickly, even in the fridge. The FDA recommends throwing away any leftover formula from a feeding rather than saving it for later. There is no safe window for refrigerating a half-finished bottle.
This can feel wasteful, especially with a newborn who only takes an ounce or two at a time. One practical workaround is to pour smaller amounts into the bottle and keep the rest of the prepared formula stored separately in the fridge. If your baby finishes and still seems hungry, you can pour more from the stored supply.
Why Refrigeration Matters
Powdered infant formula is not sterile. It can harbor a bacterium called Cronobacter that thrives in dry environments and is particularly dangerous for infants under two months old, premature babies, and those with weakened immune systems. Cronobacter infections are rare, but they’re serious. They can cause bloodstream infections, meningitis, brain abscesses, and in some cases, death.
Refrigeration slows bacterial growth dramatically, which is why getting prepared formula into the fridge quickly matters. The bacteria don’t stop multiplying entirely at fridge temperatures, though, which is why even refrigerated formula has a 24-hour limit. Keeping your fridge at or below 40°F (4°C) is important for all food safety, formula included.
For high-risk infants (under two months, premature, or immunocompromised), the CDC recommends using ready-to-feed liquid formula instead of powdered. Liquid formula is manufactured to be sterile, which eliminates the Cronobacter risk at the point of production. If you do use powdered formula for these babies, heating the water to at least 158°F (70°C) before mixing helps kill the bacteria. Cool the formula to body temperature (98.6°F) before feeding.
Warming Refrigerated Formula
Cold formula is safe to feed, but many babies prefer it warm. To heat a refrigerated bottle, place it in a bowl of warm water or hold it under warm running water for a few minutes. Swirl the bottle gently to distribute the heat evenly, then test a few drops on the inside of your wrist. It should feel lukewarm, not hot.
Don’t use a microwave to warm formula. Microwaves heat unevenly, creating hot spots in the liquid that can burn your baby’s mouth even when the bottle itself feels cool to the touch. Once you’ve warmed a refrigerated bottle, use it within the feeding or discard what’s left. Don’t reheat formula more than once or return a warmed bottle to the fridge.
Can You Freeze Formula?
Freezing prepared formula is not recommended. The FDA warns that freezing causes the formula’s components to separate, which can alter the texture and potentially affect how evenly nutrients are distributed in the liquid. Even if you thaw and shake it, the formula may not return to its original consistency. Stick with refrigeration for short-term storage and only prepare what you’ll use within 24 hours.
Quick Reference by Formula Type
- Powdered formula (mixed): Use within 2 hours at room temperature, or refrigerate immediately and use within 24 hours.
- Ready-to-feed formula (opened): Refrigerate promptly and use within 24 hours.
- Liquid concentrate (mixed): Same rules as powdered: 2 hours at room temperature or 24 hours refrigerated.
- Any bottle baby has drunk from: Use during that feeding or throw it out. Do not refrigerate.
- Unopened formula: Store at room temperature and use before the expiration date on the package. No refrigeration needed.