Supplementing With Formula: Can You Mix Breastmilk And Formula?

Learn how to start supplementing breastfeeding with formula feeding, how to safely mix breastmilk and formula in the same bottle, and tips for success with supplementing (including what to do if baby won't take the bottle).

It’s perfectly fine to supplement your breastfeeding with formula. This may even be necessary if your little one is having trouble getting enough to drink, or has trouble maintaining or gaining weight.

It’s even safe and okay to mix breastmilk and formula in one bottle, as long as you take certain precautions.

And in some cases, supplementing breastfeeding with formula feeding is even recommended by doctors.

But there are several things to keep in mind before you supplement, including so your precious breastmilk won’t be wasted.

Today, we’ll cover everything you need to know about supplementing breastfeeding with formula, including:

  • Reasons you may choose to supplement
  • Tips for getting started with supplementing
  • How to safely mix breastmilk and formula in the same bottle (and why you might not want to do this)
  • What to do if baby refuses the bottle

Reasons you may choose to supplement

There are several reasons why you may choose to supplement breastfeeding with formula. Some are your call as the mother, but other scenarios may cause your doctor to recommend supplementing.

Common reasons you may choose to supplement include:

  • Your milk supply is low, even after you've used several common techniques to try to increase it.
    • Low milk supply can happen to anyone . Don't feel ashamed if you aren't producing enough milk --- it isn't your fault, and you're doing the best you can!
  • Baby has difficulty latching onto the breast
  • Baby isn't emptying your breasts enough, or otherwise struggles to drink enough milk
  • You and baby have been separated in the hospital due to need for treatment, and it's hard for both of you to establish the breastfeeding "routine"
  • You're going back to work (or have gone back to work) and you find that pumping is difficult
  • You have a chronic illness which makes breastfeeding especially difficult and tiring
  • You've recently had surgery on your breast/s, which is making breastfeeding more challenging
  • You and your partner have decided that your partner will feed baby formula for some feeds (such as the middle-of-the-night feed) so you can get some rest
  • You want to keep breastfeeding for as long as possible, but you (and/or baby) have trouble with the process
  • You have twins or multiples, and you feel like you're not making enough breastmilk for your babies
  • You feel that exclusively breastfeeding is too overwhelming (for any reason!) but you still want your little one(s) to breastfeed some of the time

Your doctor may recommend supplementing with formula if:

  • Baby is having trouble gaining weight
  • Baby is losing weight
  • Your newborn has jaundice and needs more fluids than you can supply, since your milk is still coming in

Learn more about supplementing breastfeeding with formula in this video with Nurse Dani:

Getting started with supplementation

When to start supplementing?

  • It's best to give baby at least a month on just breastmilk, if possible, so baby becomes comfortable with the breastfeeding routine.
    • This will also help build your milk supply.
  • You can start introducing a bottle around 4-6 weeks of age at the earliest, whether that is a bottle of just breastmilk, of formula, or both.
    • This "sweet spot" age will make it more likely that baby will switch between breast and bottle with no issues.
  • There's no specific "right age" to start introducing formula to a breastfed baby, but introducing it gradually is best so baby can get used to it.
  • Also, make sure baby is happy, because introducing formula when they're upset will mean they're less likely to accept it.
    • Choose the feeding when baby is most content to introduce them to formula.
  • Start with one bottle of formula per day (or one mixed breastmilk/formula bottle per day), and continue this for at least a week.
    • Then, add in more formula per day as desired.

Can you mix breastmilk and formula in the same bottle?

If you wish, you can mix breastmilk and formula in the same bottle. You just need to follow specific steps to do this safely.

Breastmilk provides the ideal balance of nutrients for your baby.

Formula is made to provide your baby the same balance of nutrients, but does so within a very specific serving, when mixed with a certain amount of water.

If you prepare formula normally, using the standard instructions, so baby gets the right nutrition.

But if you add certain types of formula (powdered or concentrated liquid formula) directly into a bottle of breastmilk, without diluting the formula with water, this will mess up the balance of the nutrients in both the breastmilk and the formula. The mixed bottle will become too concentrated, with too much nutrients and too little water. Baby's still-developing kidneys won't be able to process all the nutrients in the mixed bottle, and this can be dangerous for baby.

Adding breastmilk to "dilute" powdered or concentrated formula, in place of water, is not safe either. This also messes up the balance of nutrients, and doesn't properly dilute the formula. It also can be dangerous for baby, as their kidneys can't handle the over-concentration of the nutrients.

Never mix undiluted powdered or concentrated formula directly with breastmilk, in any way.

Dilute the formula with water first, before mixing!

Here's how to safely mix breastmilk and formula in the same bottle:

If you're using powdered formula or concentrated liquid formula:

Prepare a serving of the formula first, in a separate bottle from the breastmilk. Follow the manufacturer's instructions (or your doctor's instructions) exactly.

The instructions will tell you how to dilute the formula with water.

First, make sure this water is either cleared as safe to drink from the tap, or boiled for five minutes and then cooled.

Then, dilute the formula with the exact recommended amount of drinking water.

Once you've properly prepared (diluted) the formula as normal, you can safely add the formula to a bottle of breastmilk.

If you're using "ready-to-feed" formula:

"Ready-to-feed" formula is already diluted. So, it's safe to mix "ready-to-feed" formula with breastmilk, directly out of the container.

Should you mix breastmilk and formula in the same bottle?

Even though there are safe ways to mix breastmilk in the same bottle, you might not want to do that. You might prefer to alternate breastfeeding (or bottles of only breastmilk) with bottles of only formula.

Breastmilk is precious, especially if your supply is already low! If you mix breastmilk and formula in the same bottle, there's the risk that your breastmilk could go to waste if baby doesn't take the entire bottle.

To prevent tossing out breastmilk, offer baby as much breastmilk as you can first. Then, offer them formula until they are satisfied.

This will also ensure that baby will get the maximum benefit from breastfeeding. Even though breastmilk and formula are virtually identical in terms of nutrients, breastmilk offers immune-boosting properties that formula doesn't.

Tips for supplementation success

Making bottle feeding like breastfeeding is key to supplementation success. This consistency will help baby switch back and forth between the bottle and the breast with no issue.

  • Consider the paced bottle feeding technique, which is aimed at replicating the "feel" of breastfeeding.
  • Choose a bottle with a slow-flow nipple, to match the flow of your milk from the breast. Consider choosing a breastfeeding bottle, with a nipple shape that's designed to mimic the shape of your breast, as well.
  • Make eye contact with baby and hold them skin-to-skin, as you would during breastfeeding.
  • Switch the sides on which you offer the bottle.

And remember that frequent breastfeeding (or pumping), where your breasts get completely emptied, is key to breastmilk production.

  • This is especially key during supplementation: the more milk that's removed, the more you'll produce. It's all about "supply and demand!"

What if baby won't take the bottle?

Usually, babies switch back and forth between breast and bottle with no issue. The tips above will encourage baby to be comfortable switching.

But if baby starts to refuse the bottle, try waiting longer between feedings so baby is hungry when you present the bottle. Changing the temperature of formula, or dribbling a bit if breastmilk on the formula bottle nipple, may also help.

You could also have your partner offer the bottle when you are out of the room or house (as baby might associate you with the comfort of breastfeeding).

Or, try these other tips to overcome bottle refusal and minimize "nipple confusion."

Key takeaways for moms

Don't be discouraged if you feel like you need to supplement breastfeeding with formula. You're doing an amazing job!

Remember: Never mix breastmilk with undiluted powdered formula or concentrated liquid formula. Dilute the formula first, so it's safe for baby.

Make the formula feeding times like your breastfeeding routine, so baby will be more comfortable and you'll get the same bonding time.

And be sure to follow best practices for maintaining or increasing your milk supply when you supplement. Along with the supplementation, this will help you keep breastfeeding longer, even if your supply is low or baby struggles with breastfeeding.

Introduce Allergens Safely and Easily with Ready. Set. Food!

All health-related content on this website is for informational purposes only and does not create a doctor-patient relationship. Always seek the advice of your own pediatrician in connection with any questions regarding your baby’s health.

These statements have not been evaluated by the Food and Drug Administration. Products are not intended to diagnose, treat, cure or prevent any disease.  If your infant has severe eczema, check with your infant’s healthcare provider before feeding foods containing ground peanuts.