How Long Can Formula Sit Out Once Prepared?

Last Updated: 
July 18, 2024
 | 
8
 minutes read
Written by
Amanda Kule
Parent Contributor
Medically reviewed by
Arik Alper, MD
Pediatric Gastroenterologist and Aerodigestive Specialist

For the first year of your baby’s life, formula and/or breast milk are their biggest source of nutrients.  

Because babies who drink formula drink a lot of it, parents often have questions on how to make sure the formula they serve is prepared safely and how long can formula sit out once prepared. Since formula can come in different forms, including powdered form, and ready-to-feed formula, the guidelines for preparing each type of formula may slightly differ.

In this article we review how long formula is good for, whether it be in the fridge or room temperature, give advice on when you should throw out a bottle of formula, and share tips for how to share formula correctly. We will also review some of the differences between serving prepared formula and ready-to-feed formula.

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How Long Does Formula Last at Room Temperature?  

Infant formula, just like most food or beverage items, can go bad if left out at room temperature for too long. How long formula can sit out depends on if your baby has drunk out of the bottle yet.

  • You baby should only drink prepared formula at room temperature if it’s within two hours of being made.  
  • If your baby already starts drinking from the bottle and doesn’t finish, it should be thrown out after one hour.  
  • Even if your baby hasn’t drunk from the bottle, the formula should still be thrown out after two hours.  
  • Don’t put a bottle back in the fridge if your baby hasn’t finished it – after one hour, throw it away.

Before your formula is prepared, it can stay out at room temperature in a cool, dry place.  

The U.S. Center for Disease Control and Prevention says most powdered formulas for babies should be used within one month of when you open the container. Make sure to check the label in case it says anything different.  

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How Long Is Formula Good for in the Fridge?  

If you prepare powered formula for your baby with water and they don’t drink it, or you prepare formula in advance and want to save it in the refrigerator for later, it can be fed to your baby within 24 hours. After one day in the fridge, prepared formula can grow bacteria that becomes unsafe for your baby.  

If you open a bottle of ready-to-feed formula for your baby, it should be covered in the fridge and used or thrown out after 48 hours.  

Expert tip: If you are going out and need to bring pre-made formula with you, you can put pre-made formula in a cooler bag with a cold source. Prepared formula should never be left for more than two hours without a cold source.  

How Long is Formula Good Once Mixed?

If you’re preparing a bottle with powdered formula and water, it should be used within one hour if your baby has drunk from it. If kept at room temperature, an unused bottle of prepared powdered formula should be thrown out after two hours.

If you mix your formula in advance and put it in the refrigerator, it should not be served to your baby after 24 hours.

Common question from parents: Can I leave a bottle ready for a nighttime feed?

If your baby still feeds in the middle of the night, it’s best to mix the formula right before you give it to them, or warm it from the fridge on-demand if it’s prepared already. This is because formula should not sit out overnight in room temperature.

If you’re trying stop the middle-of-the-night formula bottle because your baby no longer needs it (but still wakes from habit), the Smart Sleep Coach by PampersTM app can help get your baby on a sleep schedule that promotes longer sleep stretches and reduces night wakings. If nighttime formula bottles are a sleep crutch for your baby, take this free 3-minute sleep quick to get a personalized plan to break that habit.  Some babies sleep better in as little as a few days – and the app offers one week free! 

How Long is a Bottle of Formula Good for Once Your Baby Drinks from It?  

If your baby is drinking any type of formula, including ready-to-feed formula, or prepared powdered formula, it should be thrown out after an hour if your baby has already taken sips from the bottle.  

This is to prevent any bacteria that contaminates the bottle from getting your baby sick.

Can You Reheat Formula?  

The safety of reheating formula depends on if your baby has drunk it yet or not.

You can reheat formula if it has been stored in the refrigerator properly and has been stored in a container that your baby has not drank from yet. You should not reheat the formula if your baby has already taken a drink from the bottle.  

There are two recommended ways to reheat formula.  

  1. Under Hot Water. You can put the bottle until hot running water from the sink until it’s warmed.
  1. On the Stove: Heat water in a pan and once hot, remove it from the stove and soak the bottle in it until warm.

Always shake the bottle after you warm it and make sure to test the formula before you feed your baby to make sure it’s not too hot. You can test whether formula is too hot by shaking a few drops on the top of your hand. Formula should be around body temperature 98.6 degrees Fahrenheit (37 degrees Celsius).

Experts recommend that you do not microwave formula – it can reheat inconsistently and end up burning your baby’s mouth.

Does Unopened Baby Formula Expire?  

Just like with any food or beverage product, unopened baby formula can expire.  

Make sure to check the use by date on the package of your baby formula. To keep unopened baby formula from expiring, always store the unopened formula container in a cool and dry place inside. It’s not recommended you keep unopened formula in your car, garage, or outside.

Once your baby starts to be introduced to solids, they may start drinking less formula and you may be left with unopened formula that’s not yet expired. Some parents with babies who are ready to stop drinking formula give away unopened unexpired formula to friends or others in need.

Final Thoughts

What you feed your baby is incredibly important and for the many babies that drink formula, proper storage is key to keeping your baby healthy.  Until babies drink water and eat solids, they get who get most nutrients and hydration from formula – so proper prep is key!

As parents, we understand you want to make sure everything you feed your baby is safe. By following the guidance in this article around how long formula can stay out, you are reducing the risk that any of your baby’s bottles are contaminated or unsafe.  

If you have any concerns about your baby’s feeding habits or what formula they drink, speak to your pediatrician.

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FAQs:

If your tap water is safe, you can make formula with tap water. Fluoride is added to tap water in many places, which is a good thing for their teeth. The CDC says you can swap out bottled water occasionally to minimize any slight white lines on their teeth. If you baby is under two months old, is immunocompromise, or was born prematurely, speak to your pediatrician about if you should prepare formula with boiled water.

You can prepare powered infant formula ahead of time and store it in the fridge for up to 24 hours. After 24 hours, you should throw it away. If you want to prepare a bottle for a night feed, you can either measure out the powder formula and water separately and mix it on demand, or prepare the formula and store it in the fridge. You should not leave formula out in room temperature for more than two hours, less if your baby has already taken a sip.

If your baby prefers their bottle of formula warm, you can warm it by running it under hot tap water or by letting it sit in hot water. Always test the formula on the top of your hand before feeding it to your baby. The formula should be body temperature, which is 98.6 degrees Fahrenheit (37 degrees Celsius). Your baby can also drink their formula cold if they prefer that.

If formula has been sitting out for 3 hours, it has an increased risk of being contaminated with bacteria that could make your baby sick with a stomach-ache. If you’re not sure how old the formula is, it’s better to make a fresh bottle.

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How We Wrote This Article

The information in this article is based on the expert advice found in trusted medical and government sources, such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.

Sources

American Academy of Pediatrics Healthy Children.org, “How to Safely Prepare Baby Formula With Water”

Center for Disease Control and Prevention, “Infant Formula Feeding”

Center for Disease Control and Prevention, “Infant Formula Preparation and Storage”  

Mayo Clinic, “Infant and Toddler Health”

U.S. Food and Drug Administration, “Once Baby Arrives - Food Safety for Moms to Be

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