How Long Is Formula Good For After Opening? (Mixed, Unmixed, & More!)

Baby formula is a convenient alternative to breastfeeding. It can be quickly mixed and stored for feedings without sacrificing the nutrients your baby needs, but it’s also a manufactured food product with an expiration date. How long is powdered formula actually good for?

Powdered formula should be stored in a cool, dry place and used within one month of opening. After mixing, refrigerate the formula immediately if not ready to use. The prepared formula can be left out for up to 2 hours, but, once feeding has begun, it should be discarded after 1 hour. Any leftover formula should not be refrigerated for later use.

Read on to learn more about how long formula is good for after opening, and the safest ways to mix and store formula to keep your baby healthy.

How long is powdered formula good for once opened?

Powdered formula is a convenient, nutritious alternative to breastmilk. It can be especially helpful for parents who either choose not to breastfeed or have a limited milk supply and for babies who have lactose intolerance or an allergy. Especially if you are not using powdered formula as your baby’s primary source of nutrition, you may wonder how long the can of formula will last once it’s been opened.

The major brands of baby formula indicate on their websites that powdered formula should be kept tightly closed in a cool, dry place. Once opened, it needs to be used within 30 days. After this time, the nutritional components begin to degrade, meaning that your baby will not be receiving the necessary nutrition and could lead to malnutrition.

Powdered baby formula isn’t sterile. For this reason, it should be carefully reconstituted and held at appropriate temperatures to prevent the growth of bacteria. Practicing proper hygiene will also help prevent any foodborne illnesses.

Proper mixing, storage temperature, and storage times should also be followed to prevent bacterial growth and possible illness.

Parents should remember to use the powdered formula per the manufacturer’s instructions and observe the general safety guidelines provided by health organizations such as the FDA and the CDC.

Mixed at room temperature

Baby formula mixed at room temperature can go bad. The process of mixing formula can introduce harmful bacteria into the liquid. The nutrient-rich environment can make it easy for that bacteria to grow.

Bottles mixed from powdered formula and kept at room temperature should be discarded after no more than 2 hours. This prevents any harmful bacteria that may be present from multiplying and making your baby sick. Ready-to-feed bottles left at room temperature are also good for up to 2 hours before needing to be thrown out.

Always follow the manufacturer’s directions for the formula you are using. The information listed here is the generally accepted guidelines.

Does formula really go bad after an hour?

You may have heard that baby formula goes bad after an hour, but is that really true?

If you haven’t started feeding within 2 hours of mixing formula and it’s sitting at room temperature, you should refrigerate or discard it immediately. Prepared formula at room temperature should be used within 1 hour after feeding begins. Saliva from your infant can introduce bacteria that flourish in the nutrient-rich formula. 

To lower the risk of contamination, the FDA recommends preparing only enough for a single feeding at a time. Mixing formula in large batches (such as a pitcher) offers a greater opportunity for bacteria to grow. If you mix a large batch, immediately divide it into multiple bottles and refrigerate to reduce potential risk.

In addition, make sure to wash your hands thoroughly with soap and water before preparing bottles. Ensure the bottles and all components (nipples, rings, etc.) are also clean.

Can you put leftover formula in the fridge?

If your baby fell asleep during their feeding or otherwise didn’t finish, can you put it back in the refrigerator so they can finish it later?

Leftover formula (powdered or liquid) that remains in the bottle and is not consumed during a feeding should be discarded immediately.

Your baby’s saliva introduces bacteria into the formula that can continue to grow. Be sure to clean and sanitize the bottle again before the next usage.

Mixed and warmed up

Microwaves are not recommended for warming bottles due to the possibility of uneven heating (hot spots). Overheated milk from hot spots can cause severe burns to the baby’s mouth and throat.

Heated bottles with both powdered and ready-to-drink formulas should be used within 1 hour. After 1 hour, any remaining formula should be discarded to prevent contamination and possible illness.

Safely heat bottles by holding them under running warm (not hot) water for 2-3 minutes, or by placing them in a bowl of warm water for about 2 minutes.

You can also use a bottle warmer, which can be a lifesaver for overnight feedings.

How long can you keep milk in a bottle warmer?

Leaving a bottle warmer on overnight can be a fire hazard.

Many bottle warmers heat water with steam. If the water evaporates and the bottle warmer is not shut off, it can cause a fire.

Bottles should be kept in a warmer for no more than 30 minutes to allow time for feeding before the formula should be discarded. Warmed bottles should be used within 1 hour.

It’s best to start warming your baby’s bottle as soon as they wake up. You can also change your baby’s diaper while the bottle warms.

How long can formula sit out after being warmed?

Say you wake up in the middle of the night and your baby is crying for a bottle. You stumble to the kitchen and warm up a bottle of formula, but, by the time it’s ready, your baby has miraculously fallen back to sleep. Is it okay to keep the bottle out until your little one wakes back up hungry?

Baby formula that has been warmed should only be allowed to sit out for 1 hour before being discarded. The warmer temperature creates the perfect environment for harmful bacteria to grow, whether it has been exposed to outside contaminants (aka your baby’s mouth) or not.

Never rewarm formula that has been sitting at room temperature for more than an hour. And never refrigerate formula that has been warmed for use later.

Can you refrigerate formula after warming it?

If your baby has decided they don’t want to eat after all, you’ll need to discard the formula if you’ve already warmed it.

Formula that has previously been warmed or that reaches room temperature should never be re-refrigerated. Bacteria can begin to grow and some bacteria can live even during refrigeration. 

Mixed and refrigerated

Mixed and refrigerated bottles can be a huge time saver for parents.

Once mixed, powdered or liquid concentrated formula should be put in capped bottles or a tightly covered container and refrigerated immediately.

Making formula bottles in advance

Make sure you only mix and refrigerate what you can use within 24 hours. Opened ready-to-feed bottles can be refrigerated for up to 48 hours.

If you’re making up formula bottles for travel, the same timing applies so long as the bottles are in a cooler with enough ice packs to keep them cold to the touch until they can be refrigerated.

To keep track of your prepared formula bottles:

  • Label bottles with post-its or painter’s tape, or set an alarm on your phone to remind you of the date and time you prepared the bottles.
  • Place bottles toward the back of the refrigerator where it’s the coldest.
  • Chill bottles you’ll take “on the go” in the back of the refrigerator for an hour before leaving home.
  • Rotate bottles so the newest ones are in the back and the oldest bottles are toward the front.

These tips are especially important to keep in mind if you’ll be dropping your little one off at daycare.

How to store formula milk for night feeds

For both powdered and ready-to-feed formulas, mix bottles before going to bed and store them in a cooler bag with ice packs or in the refrigerator.

Unused mixed bottles with powdered formula are good for 24 hours in the refrigerator, a mini-fridge in the nursery, or in an insulated cooler bag with enough ice packs to keep them cool to the touch all night.

Unmixed in the container

Dry, unmixed formula stored in its original container is good for 30 days from the date it is opened.

It should be stored in a cool, dry place with the lid tightly sealed for best results. Make sure to check the expiration date or “use by” date on the container as well as that date will supersede any supposed expiration based on the open date.

Does baby formula have an expiration date?

Like most foods, baby formula will expire if left on the shelf – even unopened – for too long.

Be sure to check the formula container for the expiration or “use by” date before you purchase it. Avoid using formula after the stamped expiration date on its packaging.

Even though most babies go through formula quickly, make sure you have enough time to use it before the expiration date.

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