Can You Mix Breast Milk and Formula?
Many new parents opt for combination-feeding (aka giving baby both breast milk and formula). It’s a great path for those who can’t exclusively breastfeed, but still want to give baby the benefits of breast milk. If this is you, you’ve likely considered mixing breast milk and formula in the same bottle. But it’s possible you’ve also wondered: Can you mix breast milk and formula safely? Experts say you can, but there are a few important considerations to keep top of mind. Read on for everything you need to know about how to mix breast milk and formula.
In this article:
Can you mix breast milk and formula in the same bottle? The benefits of mixing breast milk and formula The downsides of mixing breast milk and formula How to mix breast milk and formula What are the rules for mixing breast milk and formula? How long is breast milk and formula mixed good for? Can you mix formula with breast milk instead of water?
In short, the answer is yes: Mixing breast milk and formula in one bottle is possible.
That said, some experts don’t recommend this method. “Generally speaking, I’d keep them separate,” says Kathleen Kendall-Tackett, PhD, IBCLC, a health psychologist, clinical associate professor of pediatrics at Texas Tech University Health Sciences Center and author of Breastfeeding Doesn’t Need to Suck: How to Nurture Your Baby and Your Mental Health. If you choose to combination-feed, she suggests either feeding at the breast and topping off with formula as necessary, or alternating between breast milk and formula.
Some moms opt for mixing breast milk and formula because they have low milk supply but still want to give their babies some breast milk. “Every bit is beneficial,” says Kendall-Tackett. If you exclusively breastfeed and want to start supplementing with formula—or eventually switch to formula altogether, mixing breast milk and formula could help baby with the transition. “Mixing can help babies get used to the taste and texture of formula,” says Jennifer Shu, MD, FAAP, a pediatrician with Children’s Medical Group, P.C. in Atlanta and co-author of Heading Home with Your Newborn.
While there are benefits to mixing breast milk and formula in the same bottle, one downside is that you might waste precious breast milk if you don’t use the full bottle before it goes bad. What’s more, you have to use up formula a lot quicker than breast milk. (A bottle of formula—alone or mixed with breast milk—is officially safe to keep in the fridge for 24 hours, versus breast milk alone, which can be refrigerated for up to four days, according to the Centers for Disease Control and Prevention (CDC).
Additionally, adding formula into baby’s routine might mean you’re breastfeeding or pumping less, which can, in turn, decrease your supply, according to Kendall-Tackett.
Mixing breast milk and formula is relatively straightforward: “Mix the formula first as you normally would, then add some breast milk to the bottle,” says Shu.
If you’re using powder (or concentrated) formula, start by measuring formula and water as directed on the label, according to UPMC Health Beat. Then, prepare it according to the directions. Ready-to-use formula is, as the name suggests, ready to use straight out of the bottle.
Once you’ve prepped the formula, you can use it in any proportion to breast milk that works for you and baby. If baby’s trying formula for the first time, for example, you might want to add an ounce of formula to several ounces of breast milk. If, on the other hand, your baby is already used to the taste of formula, you may want to use mostly formula to stretch out precious pumped milk. Swirl the bottle before serving to mix any separated fat from the breast milk back in with the water, advises the CDC.
Once you’ve learned how to mix breast milk and formula, there are a few things to keep in mind. It’s perfectly safe to serve mixed breast milk and formula cold, “but some babies don’t like it that way,” says Kendall-Tackett. If baby balks at cold milk, you might need to warm their bottle. Set the prepared bottle in a container of warm water or use a bottle warmer for several minutes. Avoid heating milk in the microwave, as it could result in hot spots that could burn baby’s mouth, says the CDC. Always test a few drops on your wrist before serving.
If baby is under 2 months old, born preterm or has a weakened immune system, you’ll need to take extra precautions to protect them from bacteria in powder formula, says the CDC. Boil the water you’re using to prepare the formula, add the powder formula about five minutes later and wait until the bottle has cooled before feeding baby.
When it comes to storing your mix of breast milk and formula, Kendall-Tackett says you can follow the guidelines for formula storage. The CDC and Food and Drug Administration (FDA) recommend refrigerating prepared formula for a maximum of 24 hours. The FDA also warns against storing formula in the freezer, as freezing may cause the ingredients to separate.
As long as baby hasn’t had a sip from a bottle containing a mix of formula and breast milk, you can keep the mixture in the fridge for 24 hours, as per the CDC’s guidelines for formula storage.
As soon as baby feeds from a bottle, the CDC says you’ll need to dump any unused milk within an hour: Bacteria can grow when formula combines with baby’s saliva.
When preparing powder or concentrated formula for baby, don’t use breast milk instead of water, says Kendall-Tackett. Formula already has more protein than breast milk, she explains, and adding breast milk without water could increase the concentration of protein and calories and potentially stress baby’s kidneys. Additionally, too little water in powder formula could cause baby to become dehydrated, according to the CDC. “Some pediatricians will recommend doing this if a baby isn’t growing well, but check with your baby’s doctor for the right amount,” says Shu.
Please note: The Bump and the materials and information it contains are not intended to, and do not constitute, medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances.
Kathleen Kendall-Tackett, PhD, IBCLC, is a health psychologist, clinical associate professor of pediatrics at Texas Tech University Health Sciences Center and author of Breastfeeding Doesn’t Need to Suck: How to Nurture Your Baby and Your Mental Health.
Jennifer Shu, MD, FAAP, is a pediatrician with Children’s Medical Group, P.C. in Atlanta and co-author of Heading Home with Your Newborn. She earned her medical degree at the Medical College of Virginia at Virginia Commonwealth University.
Nemours KidsHealth, Feeding Your Newborn, February 2021
La Leche League International, Mixing Milk
Centers for Disease Control and Prevention, Infant Formula Preparation and Storage, May 2023
Centers for Disease Control and Prevention, Proper Storage and Preparation of Breast Milk, January 2022
UPMC Health Beat, Can You Mix Formula and Breast Milk?, June 2023
U.S. Food and Drug Administration, Infant Formula: Safety Do’s and Don’ts, May 2023