Feeding Your Baby

Supplementing With Formula: Can You Mix Breast Milk and Formula?


As soon as you welcome your baby into the world, you’re bombarded with so much talk around whether or not you’ll breastfeed or formula feed, almost as if the decision has to be one or the other. You may be wondering, can you mix breast milk and formula? The good news is that you can. Mixing breast milk and baby formula together gives your baby a taste of both! 

Combo feeding, which involves giving a baby a mix of some breastmilk and some formula, has a ton of benefits, especially for parents and is an excellent alternative to breastfeeding exclusively. In fact, it can often extend the breastfeeding experience for most women. It involves either breastfeeding or pumping and giving a child a bottle of just breast milk along with bottles of just formula or mixing the two milk types into the same bottle. 

For feeding a baby, both breast milk and infant formula are nutritionally complete ways to do so, but there are some differences between them. “Breast milk is easy to digest, and contains live cells, specific enzymes and antibodies to help fight infections, growth factors, and prebiotics,” says Dr. Lauren Crosby, M.D., board-certified pediatrician and Bobbie Medical Expert. “Infant formula is modeled after breastmilk and, over time, has evolved with the addition of more components to mimic breast milk.” Though formula does not match breast milk’s ingredient makeup completely, it does provide all the essential nutrition a baby needs to grow and thrive. 

Mixing Breast Milk and Formula by Combo Feeding

If you’re combo feeding, you’re supplementing your child’s intake of breast milk with formula to some degree—and this might look different for every mom and baby. For example, you might be breastfeeding most of the time and only giving your baby a bottle of formula at night or you might be formula feeding most of the day and only nursing just before bed. The list of reasons why a parent might opt to combo feeding is practically endless, but often includes low breast milk supply, high demands of breastfeeding or family or work schedules that don’t align with exclusive breastfeeding.

There are plenty of benefits to combo feeding, including faster feeding. “Breastfeeding can take up to an hour, so if a parent is in a rush and has not had time to breastfeed or pump breast milk, formula can be given in a bottle instead, as it takes much less time,” says Dr. Crosby. There’s also the peace of mind that comes with you knowing that, if you don’t have enough breast milk, there is something available to feed the baby and the parent does not need to worry about the baby’s nutrition. 

Other family members can also take part in feeding the baby, which Dr. Crosby points out, can free up the breastfeeding mother to spend time with her other children, catch up on some items on her to-do list or practice some much-needed self-care. 

4 Considerations When Combo Feeding

When combo feeding, there are a few important considerations you should make. Here, Dr. Crosby shares some of the most important things to consider. 

1. Protecting your milk supply

If a parent plans to breastfeed, even if they aren’t sure they’ll do it for too long or are confident they want to give bottles too, it’s a good idea to establish your milk supply from the start and ensure the baby has a proper latch. During this period of time, Dr. Crosby recommends nursing 8-10 times a day. Once that has occurred which can take at least 2 weeks, then it is OK to introduce a bottle of formula here and there when needed, according to Dr. Crosby. “There are cases where a bottle has to be introduced earlier, often for medical reasons such as the baby has lost too much weight, is dehydrated, has low blood sugar or has jaundice, where a bottle is used temporarily to get through the medical issue before full breastfeeding can resume.” 

2. Refusing the bottle

Sometimes a baby turns their nose up at the bottle no matter how hard you try to encourage it. This is one of the reasons lactation consultants recommend introducing the bottle early on, starting around 2 weeks old and definitely by about 6 weeks old. “It is also best if someone other than the breastfeeding parent gives the bottles,” suggests Dr. Crosby. “The baby may be more willing to take them.” 

3. Latching

Most of the time, a young infant is still very open to breastfeeding even when they’re also being offered the bottle, but this is not always the case. If you run into any issues with your baby’s latch, it’s a good idea to contact a lactation consultant who can help make any necessary adjustments and offer helpful tips to encourage a better latch and smoother feedings. 

4. Change in stools

When you add in formula, you can expect a change in the quality and quantity of stool that your baby passes, notes Dr. Crosby. “Typically, formula-fed babies have less frequent stools, which is perfectly normal, but can sometimes make parents concerned,” she says.

Mixing Breast Milk and Formula in the Same Bottle

If you’re combo feeding, you might be wondering if you can mix breast milk and formula in the same bottle. Here’s what you need to know if you plan on mixing the two. 

How do you mix breast milk and formula in the same bottle?

You can make a combo feeding cocktail, according to Dr Crosby, by following these steps:

  1. Make the formula bottle as per your brand instructions
  2. Shake up the formula bottle
  3. Add the breast milk
  4. Shake it up!

Is it safe?

Lucky for you, the answer is yes! It is perfectly safe to mix the two in the same bottle. The best way to do this is to first make formula based on the specific directions that come with the specific formula to the volume they want, shake, and then add the breast milk and shake, according to Dr. Crosby. 

Is it possible to give baby too many nutrients?

No— as long as you follow the instructions on a can of formula. Dr. Crosby points out that both breastmilk and formula are nutritionally complete for infants. “Formula is based on breastmilk so the nutrition content is not an issue,” she adds.

When should parents consider mixing the two milk types?

There’s no reason to mix breast milk or formula unless it is more convenient for you. Sometimes you may have breast milk on hand that you need to use and may want to add in some formula to create more milk. It is often considered easier and faster to give one bottle at a feed rather than two separate bottles containing one breastmilk and one formula, notes Dr. Crosby. 

Are there any reasons why parents should avoid mixing milk types?

The only reason to avoid mixing milk types is to make sure that you’re not wasting the breast milk. Pumping breast milk requires time and energy, so you want to make sure that the baby gets the breastmilk. “If the two are mixed together and the baby does not finish the bottle then some breast milk is wasted,” says Dr. Crosby. 

3 Considerations When Mixing Milk in the Same Bottle

  1. Follow safe breastmilk storage

Per the CDC’s guidance for Proper Storage and Preparation of Breast Milk, freshly pumped breast milk can remain at room temperature (up to 77 degrees F ) for up to 4 hours. It can be stored in the refrigerator for up to 4 days and in a freezer at 0 degrees F or colder for up to six months. Thawed previously frozen breast milk can sit at room temperature for up to 2 hours.  

  1. Follow safe pre-mixed formula storage

Prepared infant formula should be used within 2 hours of preparation or within one hour from the start of a feeding, notes Dr. Crosby. If it is not used within 2 hours of preparing, she recommends it be stored in the refrigerator and used within 24 hours. 

  1. Avoid over-concentrating nutrients

“For the safety of an infant, infant formula must be prepared per its own package directions first before adding it to breast milk,” says Dr. Crosby. “If powdered or concentrated infant formula is added to breast milk before it is properly prepared, it can be dangerous for the baby, since infants’ kidneys are not mature enough to handle the nutritional load without the proper water balance.”  


Why should you not mix breast milk with formula?

Mixing breast milk with formula is safe, but there are occasions where you may want to keep the two separate. For example, if you’re not sure your child will finish the combination of the two milks, you will be wasting the breast milk, since it has to be thrown out within an hour of your child drinking from the bottle. 

Can mixing formula and breastmilk cause upset stomach?

If your baby tolerates both breastmilk and formula separately, then mixing them together should not cause an upset stomach, according to Dr. Crosby. If, for any reason, your baby does have an upset stomach, try burping them or bicycling their legs to alleviate any gas that might be built up. 

Mixing both breast milk and formula is not recommended if the baby is not going to finish the bottle, according to Dr. Crosby. “If your baby doesn’t finish the bottle, the breast milk will be discarded when the leftover contents of the bottle are thrown out,” she says. “Also, mixed feeding might not be recommended because of concerns that parents may not do it properly.” 

Which formula is closest to breast milk?

Dr. Crosby recommends looking for a formula that has lactose as its first ingredient and a whey:casein ratio that is closest to breastmilk.

Does mixing breastmilk and formula cause constipation?

Due to the fact that formula-fed babies tend to pass fewer stools than breast milk-fed babies, constipation may occur when you mix them together. However, Dr. Crosby points out that mixing the two milks together often provides better stool frequency than formula alone. 

Is breast milk really that much better than formula?

While there is quite a significant amount of research to support the benefits of breast milk, modern-day formula is an excellent second option for providing nutrition to your baby. If you have any concerns regarding breast milk being more beneficial than baby formula, consider talking to your pediatrician who can likely alleviate your worries. 

Will formula make my breastfed baby sick?

No. Infant formula is made to mimic breast milk and provide all the proper nutrients a baby needs to grow and thrive.  

Does formula taste the same as breast milk?

The taste of breast milk tends to vary based on a mother’s diet while formula always tastes the same. This can have its benefits, as your baby is less likely to turn their nose up on a certain feeding occasion as a result of taste change. In general, there is no way for formula to exactly mimic the taste of breast milk, according to Dr. Crosby. 

Takeaways about combo feeding:

Combo feeding is a great feeding option for parents looking to share the nourishment of breast milk while supplementing with formula. Combo feeding can be done to extend the breastfeeding journey. It’s even a great way for the partner to take care of night time feedings so that mom can get some extra sleep yet continue to breastfeed during the daytime. Whichever amount of breast milk versus formula works best for you in a win in our parenting book.

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant's pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant’s pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

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Meet the Expert

Jenn Sinrich

Jenn Sinrich is an experienced writer, digital and social editor and content strategist in Boston, Massachusetts. She's written for several publications including SELF, Women's Health, Martha Stewart Weddings, Reader's Digest, PureWow, and many more. She covers various topics, from health and fitness to love and sex.