Once you open a can of powdered infant formula, it stays good for about one month. That’s the standard across most brands, and the CDC recommends writing the date on the lid the day you open it so you don’t lose track. But “how long is formula good for” has a few different answers depending on whether you’re talking about the unopened can, the opened powder, or a bottle you’ve already mixed.
Opened Powdered Formula: One Month
Most powdered infant formula needs to be used within four weeks of opening the container. After that point, the powder can lose nutritional quality and become more vulnerable to contamination. Always check the label on your specific brand, since some may have slightly different timelines, but one month is the industry norm.
Store the open can in a cool, dry place with the lid tightly sealed between uses. Humidity and heat speed up degradation, and moisture getting into the powder creates conditions where bacteria can grow. Keep the scoop clean and dry, and avoid setting the lid or scoop down on countertops or other surfaces that could introduce germs into the container.
Unopened Formula: Check the Use-By Date
The FDA requires every container of infant formula to carry a “use by” date. The manufacturer guarantees both the nutrient content and the safety of the formula only up to that date. Unlike many other food products where expiration dates are more of a quality suggestion, this one matters. Don’t use formula past its use-by date, even if the container has never been opened.
Mixed Formula: A Much Shorter Window
Once you mix powdered formula with water, the clock speeds up considerably. A prepared bottle that hasn’t been fed to your baby can sit at room temperature for up to two hours. If you make bottles ahead of time, store them in the refrigerator and use them within 24 hours.
If your baby has already started drinking from a bottle, the timeline shrinks further. Saliva introduces bacteria into the formula, and that bacteria multiplies quickly at room temperature. A partially finished bottle should be used within one hour of the feeding starting. After that, throw it out. Reheating it or putting it back in the fridge won’t make it safe again.
Ready-to-Feed and Liquid Concentrate
Ready-to-feed formula follows different rules once opened. These liquid products need to be refrigerated immediately after opening and used within 48 hours in most cases, though you should check the label on your specific product. The advantage of ready-to-feed is that it’s sterile until you open it, which makes it a safer option for newborns or babies with compromised immune systems. Once opened, though, it’s more perishable than dry powder.
Why These Timelines Matter
Powdered formula is not sterile. It can contain bacteria, including Cronobacter, an organism that lives naturally in dry environments. While infections are rare, they are severe when they occur. Around 20% of infants in the United States who develop meningitis or bloodstream infections from Cronobacter die. Infants younger than two months old face the highest risk.
Cronobacter can enter formula in several ways: during manufacturing, from a contaminated scoop or lid, from the water you mix it with, or from a bottle that wasn’t properly cleaned. Following storage timelines doesn’t eliminate all risk, but it significantly reduces the chance of bacterial growth reaching dangerous levels.
Don’t Freeze Formula
Freezing prepared formula might seem like a logical way to extend its life, but the FDA advises against it. Freezing causes the fat and other components to separate, changing the texture and potentially affecting how well your baby absorbs the nutrients. There’s no safe way to freeze and thaw formula while keeping it nutritionally intact.
Signs Formula Has Gone Bad
Even within the recommended timelines, formula can spoil if it’s stored improperly. Here’s what to look for before using any formula, whether it’s powder from an open can or a bottle you mixed earlier:
- Color changes: Fresh powder has a consistent, uniform color. Darkening or unusual spots suggest spoilage.
- Texture changes: Clumps, lumps, or a gritty texture in powder that should be fine and smooth.
- Off smells: Sour, rancid, or chemical odors are clear signs the formula should be discarded.
- Mold: Check the underside of the lid and the surface of the powder for any visible mold or mildew, especially if moisture may have gotten into the container.
- Insects: Check inside the container for any signs of pests.
If anything looks or smells off, discard the entire container. Formula is not something to take chances with, and no visual test can detect bacterial contamination that hasn’t yet caused visible changes.
Quick Reference by Formula Type
- Unopened can (any type): Good until the use-by date printed on the container.
- Opened powdered formula: Use within one month. Store sealed in a cool, dry place.
- Opened liquid or ready-to-feed: Refrigerate immediately and use within 48 hours (check your label).
- Prepared bottle, not yet fed: Up to 2 hours at room temperature, or up to 24 hours in the refrigerator.
- Partially finished bottle: Use within 1 hour of feeding, then discard.