Mixing Breastmilk with Formula - Your Questions Answered

Posted by Jane Springston on

You’d think that feeding your baby would be an easy endeavor, but it’s actually tricky business! Starting with the biggest decision - whether you’re going to feed your baby breastmilk or formula. For many parents, the choice is both! Though generally you’ll feed your baby breastmilk and formula separately, there may be times where it would work best to mix them together. But is it recommended?

Here we’ll give you the safety information you need about mixing breastmilk and formula so you can give your baby the best and healthiest breastfeeding experience possible.

Supplementing Breastmilk with Formula

At the Baby’s Brew, we believe that fed is best. So whether you’re breastfeeding your baby, exclusively pumping, formula feeding, or doing a combination of two or three, we commend you, Mama, for doing your very best. What many mamas end up doing is breastfeeding their baby as much as they can while supplementing with formula. 

According to the CDC Breastfeeding Report Card, 83% of babies start out breastfed whereas only about 47% are exclusively breastfed at 6 months. That means there are a lot of babies who are either formula fed, or at least supplemented with formula. And from time to time, parents may wonder if it’s appropriate to mix breastmilk and formula. 

Can I mix breastmilk with formula?

You may see differing opinions on whether you should mix breastmilk and formula together. According to Healthline, “Breastmilk and formula don’t have to be mutually exclusive” and they can even be mixed together. However, La Leche League suggests that it may be preferable to do separate feedings. But that’s not because it isn’t safe.  (More on that coming up.)

So, which is it? Is it okay to mix breastmilk and formula in one bottle?

Yes, you can safely mix breastmilk and formula following proper guidelines. However, you may determine that it’s best to first feed your baby the pumped breastmilk and then give them any formula required to supplement a feeding. 

The truth is that it can be more convenient to make one bottle that has breastmilk and formula combined into one bottle. An example would be if you are heading out on errands and know you’ll need to feed your baby 5 ounces of milk but only have 2 ounces of breastmilk to give them. Instead of making two separate bottles, it’s easier to just make one. 

As a mama myself who had many times where I wouldn’t pump enough to satisfy my baby, I was left with this exact choice. Do I mix the two together or feed the breastmilk first and then the formula?

There is no wrong choice about whether to keep the two separate or mix them, but instead is what works best for you and your baby. 

How to Properly Prepare a Bottle of Mixed Breastmilk and Formula

Life as a parent can be overwhelming and busy, so it’s not a surprise that lots of moms and dads are wondering if they can have a little convenience by combining breastmilk and formula into one bottle. If you choose to go this route, here are some safety considerations to keep in mind:

  • Formula should always be mixed according to the package instructions so that you have the correct ratio of formula to water for proper nutrition.

  • Adding powdered formula or concentrated liquid formula to a bottle of breastmilk without first mixing it with the correct amount of water, means your baby won't be given the correct ratio of nutrients to water. This can be unsafe for your baby.

This means that you always need to FIRST mix the powdered formula or concentrated liquid formula with the correct amount of water BEFORE mixing it with breastmilk. This ensures your baby is getting the correct amount of nutrition and water that they need.

Follow these steps to properly prepare a bottle of mixed breastmilk and formula:

  1. Use a clean, empty bottle.
  2. Put the proper amount of formula into your baby’s bottle followed by the proper amount of water (always use the manufacturer’s instructions written on the package).
  3. Mix the water and formula together.
  4. Then, you can add in your breastmilk. Just be sure that the breast milk is fresh.
  5. Mix the two together.

If you are using “ready-to-feed” formula where the formula and water are already mixed together, you will skip steps 1 -3 above. (These are also sometimes called “ready-to-use” formulas and will say to not add water.

Before feeding your baby their bottle, you may decide that it’s best to warm it up. If your baby is used to drinking warm milk, whether that be from the breast or bottle, than you’ll want to consider warming up your baby’s bottle of combined breastmilk and formula.

Heating a Bottle of Mixed Breastmilk and Formula

Though it isn’t required, generally babies prefer warm milk. Nature intended for babies to have milk at 98.6 degrees, so it’s not surprising that they may refuse a bottle of cold, or even room temperature, milk. 

In our article, “How to Safely and Effectively Warm a Baby Bottle,” we cover all the ways to safely warm a bottle of breastmilk or formula. These included using a bowl of warm water, running it under warm running tap water, or using a bottle warmer.

A bottle warmer is by far the easier choice, and a portable one like the Baby’s Brew makes it a simple process both at home and on the go. (Plus you can even choose your baby’s preferred temperature.)

You can warm a bottle of mixed formula and breastmilk in the same way. After following the above instructions for safe mixing, simply use one of the warming methods to give your baby a warm bottle. 

Never warm your baby’s bottle in the microwave. You can find out why this is a dangerous method for warming in our article, “Microwaving Breastmilk: Why It’s a No Go.” 

Why You May Choose to Keep Breastmilk and Formula Separate

Though you can safely mix breastmilk with formula, you may decide that it’s better to keep them separate. There is one major reason that some parents choose to go this route.

By not mixing breastmilk and formula together, you’re less likely to waste any breastmilk.

As discussed earlier, La Leche League recommends not mixing breastmilk and formula because if your baby doesn’t finish a bottle, you end up wasting some of the breast milk that was leftover (because you can’t save any leftover milk from a baby’s bottle). This comes from the thought that breastmilk is the optimum nutrition for babies and that it’s preferable for a baby to get as much breastmilk as they can.

For example, if you take 4 ounces of breastmilk and mix it with 2 ounces of formula, and your baby only drinks 4 ounces of the mixture, you end up having to throw the rest away. Your baby took in a combination of formula and breastmilk. If you had chosen to give your baby the 4 ounces of breastmilk in this scenario, she would have drank all of it. (You would have then given her extra formula afterwards, or would have realized she was full.)

So if you do decide to feed your baby their breastmilk and formula separately, you always want to start by feeding them your pumped breastmilk. 

In the end, only you can choose how important this is when comparing it to convenience.

Final Word on Mixing Breastmilk and Formula

Both breastmilk and formula allow a baby to thrive. If you decide that mixing the two together works best for you and your baby, then you can safely do this utilizing our steps above. Whichever you decide to do, your baby will get the nutrients they need to be healthy and happy.

← Older Post Newer Post →


  • Why does the breastmilk have to be fresh? Can you warm up refrigerated breastmilk and add that to a bottle of formula?
    Also can you mix breastmilk with cows milk?

    Sundeep on

Leave a comment

The Baby's Brew Blog


Exploring the Different Types of Child Care: Pros, Cons, and Costs

By Arianna Porcelli

As a parent, one of the most important decisions you will make is choosing the right type of child care for your child. With a...

Read more

Embrace Convenience with Baby's Brew

By Arianna Porcelli

As a new parent, you quickly learn that convenience and flexibility are your best allies in navigating the unpredictable world of parenting. One product that...

Read more