Can You Mix Breast Milk And Formula?

can you mix breast milk and formula

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When we had our son Luca in 2018, I knew nothing about milk storage. I mean, I knew how to store the cow milk I used for my coffee and cereal, but somehow it seemed like that wasn’t enough. Then, what if you are breastfeeding but also want to give formula? Can you mix breast milk and formula, or is that not safe?

A quick google searched provided me with enough info to know that yes, you can mix breast milk and formula for your baby, but just like everything else in parenthood, it is more complicated than that.

Below I will answer for you the important questions to ask yourself when making an informed decision in the matter.

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How to Mix Breastmilk and Formula.

If you want to feed your baby a combination of breastmilk and formula in the same bottle, its important that you do so the right way.

Follow these steps:

  1. Mix formula with water first.
  2. Add breastmilk last.
  3. Never use breastmilk in place of water for mixing formula as it can change the nutritional value of it.
  4. If you are using ready-made formula, you can mix them together right away.

If possible it can be better to feed baby breastmilk first and then top them off with formula after if they are still hungry. Reason being that the shelf life of these two liquids are different so you might end up having to throw away some of that liquid gold. Unfortunately this can often happen as they don’t always finish their bottle.

Sometimes they might act hungry, you make their bottle and they just take the tiniest sip before pushing it away. You just never know!

Why Would I Mix Breast Milk and Formula?

Photo by Public Domain Pictures from Pexels

Many reasons for mixing breast milk and formula are due to low supply of breast milk or when needing to transition your baby from breastmilk to formula (this can happen if they have a milk protein allergy and need soy milk). 

Supplementing your babies feedings with formula is recommended when exclusively feeding breast milk is not an option as there are important benefits to breastfeeding during the first 6 -12 months of their life. 

==>PROTIP: If you are struggling with low milk supply using a breast pump can really help<== 

When is it Best to Mix Breast Milk and Formula?

Remember that combining breastmilk and formula is safe as long as you follow the correct guidelines on how to mix and store the drink properly. If you are unsure whether this is a good option for you, I am listing a few reasons why you might want to supplement with formula during the first 12 months of your child’s life:

  • Struggling with low milk supply
  • You work full time and pumping regularly is not an option. (PS. Do you know your state’s workplace laws for pumping?)
  • Baby has a milk protein allergy and needs to go on soy milk.
  • When going away for a longer stretch and there is not enough frozen breast milk.

==>Check out these 8 Foods that will Help Increase your Milk Supply<==

What Rules Applies when Storing Breast Milk and Formula.

storing breast milk and formula
Photo by Daria Shevtsova from Pexels

Always store breast milk and in the back of you fridge. It is colder there because the temperature of the room doesn’t make it that far in when opening the doors. Storing breast milk on the door of the fridge is not recommended because it gets exposed to warmer temperatures when opening the fridge. 

Disclaimer: we often had our bottles on the door without any issues, so if you have been doing this don’t worry. Its just not preferred practice. 

Storing Breast Milk:

If you want to store your freshly pumped breast milk, it can stay in the freezer up to 6 months. Once thawed, it can stay in the back of the refrigerator up to 24 hours. 

If fresh breastmilk is refrigerated immediately it is good for 5 days. It will also stay fresh up to 24 hours in a cooler. 

Once offered bottle of breast milk it can be offered again up to 2 hours later and does not have to refrigerated again. However, if it hasn’t been offered yet, you can keep it in room temperature up to 5 hours! 

Storing Formula:

Formula that is made from powder and water can be refrigerated and used up to 24 hours. After that the nutrients in the beverage start to dissolve which can be dangerous for your babies well-being and development.

Liquid formula should be refrigerated and used within 48 hours. 

Once offered a bottle of formula, it has to be used within an hour. 

Storing Mixed Breast Milk and Formula.

If formula and breastmilk are mixed, use the storing guidelines that represent the shortest amount of time. In this case formula has to be used up faster.

The mixed bottles can stay in the refrigerator up to 24 hours. However, if left out, it should be discarded within an hour as bacteria reproduce quickly in cow milk.

Pro’s and Con’s of Mixing Breast Milk and Formula.

Making the decision to supplements your breast milk with formula might be weighing heavy on your heart, especially with all the media emphasizing the benefits of breastfeeding. Remember though that “fed is always best”, so if you are struggling to produce milk, or simply hate pumping (uhmm… me here!), supplementing bottles with formula is a decision you should make guilt-free!

==>I used a less popular electric breast pump but LOVED it. <==

It can be helpful however to make a list of positive’s and negative’s, so you can visually get an idea of what is best for you. Supplementing can absolutely make your life easier, but it comes with its limitations.


  • Takes pressure off mother to pump enough milk.
  • Is great as a plan B if stored milk is finished.
  • Mixing breast milk and formula can help transition your child to formula as flavor is a bit different. (If baby is picky like ours, slowly change the proportion of breast milk to formula in order to gently transition them).


  • Shelf life is short.
  • High chance of having to throw hard worked breast milk away if not finished.
  • Mixing it incorrectly can affect baby’s nutritional intake.

Personality Matters

Photo by Polina Tankilevitch from Pexels

Mixing breastmilk with formula can extend the amount of breastmilk you have in the freezer while not altering too much the flavor of their bottle. How you choose to feed your baby will depend on their personality, something I really didn’t fully understand before parenthood.

Easy going babies will drink whatever you give them, they will sleep when you put them down and they will play happily on the floor by themselves while smiling. On the other spectrum, high need babies are often highly opinionated about everything, like what they eat, when they sleep and often want constant one on one contact with you. 

Our son Luca was super fussy at the bottle, (guess what personality type we got.) He really only wanted the breast and although sometimes the bottle was required due to my absence, switching between breastmilk and formula would not have been easy for our family. I do think that knowing that you can mix breast milk and formula can take the pressure off many mothers, because motherhood is stressful for everyone!

What is your preferred way of feeding your little one?

Comment below!

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8 thoughts on “Can You Mix Breast Milk And Formula?”

    1. our son was super picky. I tried giving him formula once and he rejected it strongly. I think if we had no choice he’d eventually get used to it, but picky eaters can make it challenging.

  1. Its great going to your blog Stephie, you manage to answer all the important questions on each topic your blog cover. I had never heard about this option and it sounds like a great alternative when your own supply is low but you still want to continue breastfeeding. Hughs!

    1. I think some babies might give you a hard time if you shift between mixing and giving them separately. But it is a great option for many families that choose to bottle feed but still want to expose their babies to some breast milk if not being able to give it fulltime.

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