Can You Mix Breast Milk and Formula?

If you are nursing exclusively, you may be wondering if it is ok to supplement your breast milk with infant formula. Mixing formula with breast milk can provide your baby with additional liquid nourishment, and there are many reasons why moms may consider this option. Let’s dive into learning how to supplement with formula more efficiently below.

Supplement breast milk with formula

Supplementing is a combination feeding method that involves alternating breastfeeding with formula feeding by introducing formula into baby’s diet. Some common reasons you may want to supplement breast milk with formula include:

• You are going back to work
• You have a low milk supply
• Your partner would like to participate in feeding
• Your doctor recommends it

If you’re getting started and wondering how to supplement breast milk with formula, experts and lactation consultants suggest feeding your baby pumped breast milk first and then following up with a bottle of formula if he or she is still hungry. 

If you decide to supplement with formula and are concerned about making a warm formula bottle quickly for your baby, consider the Baby Brezza Formula Pro Advanced Baby Formula Dispenser. It automatically prepares a warm infant formula bottle instantly. With the press of a button, this award-winning must-have for moms automatically mixes, heats, and dispenses formula to the ideal consistency and temperature. The Formula Pro Advanced comforts your little one fast when he or she is crying and hungry. Read what this mom from Houston, Texas, had to say about preparing bottles of formula with the Formula Pro Advanced:

Such a time saver!

The Brezza has significantly cut down on the wait time to feed our son which saves us a great deal of angst when he's already flipped to hangry mode. Makes life so much easier!

Can you mix breast milk and formula in the same bottle?

According to the medical experts at Verywellfamily, mixing breast milk and formula is possible, but there are a couple of issues to keep in mind in combining formula feeds and breastfeeding:

Correct measuring is essential for safety – Infant formula is made to provide your baby with a set amount of nutrients and calories for a specific amount of water. Adding liquid formula or powdered formula before mixing with breast milk or water alters the balance of nutrients and water. This imbalance can lead to an over-concentration of nutrients, which can put stress on your baby’s immature kidneys. Avoid this situation by preparing the formula according to directions first, and then adding the breast milk. 

If you’re looking for an easy way to mix breastmilk and formula, Baby Brezza offers a super convenient product for this as well — the One Step Formula Mixer. It’s the first motorized formula mixing pitcher that you can operate hands-free. It will mix your prepared formula and breast milk perfectly, no hand cranking necessary. When you’re not using it with breast milk, you can prepare and store up to 28 oz of formula at a time. The unique mixing wand mixes formula quickly without air bubbles or clumping. The One Step Formula Mixer will save you so much time, and is not just for formula — use it for shakes and mixed drinks, too! That’s plenty of versatility for about $20. 

If you mix breast milk with formula, you could be wasting some of your “liquid gold”. - If your baby doesn’t finish the bottle, your liquid gold could be wasted. The Enfamil website states that partially consumed prepared formula should be discarded within one hour. 

Warming Breastmilk and Formula

Another great tool to have is a bottle warmer that can safely warm both formula and breastmilk. Many bottle warmers don’t maintain the nutrients in breastmilk, due to overwarming or hot spots. The Baby Brezza AirSwirl Bottle Warmer is the first of its kind on the market. It’s a waterless bottle warmer that gently swirls the bottle as it warms, keeping the formula or breastmilk moving to avoid any hot spots.

Best Practices for Transitioning to Combination Feeding

Supplementing with formula can take time. Here are some tips to make the process smoother:

• Start Gradually: Replace one feeding session at a time with formula to allow your baby’s digestive system to adjust.
• Choose the Right Formula: Consult your pediatrician to determine the best type of formula for your baby’s needs.
• Monitor Your Baby’s Response: Keep an eye out for signs of formula intolerance, such as gas, diarrhea, or fussiness.
• Maintain Breastfeeding Routines: Continue breastfeeding or pumping regularly to maintain your milk supply if desired.

Risks of Mixing Breastmilk and Formula

Mixing breastmilk and formula in the same bottle can be convenient, but it’s important to follow these guidelines to ensure safety and nutrition:

1. Nutritional Dilution

Mixing powdered formula directly with breast milk—rather than preparing the formula with water first—can alter the intended nutrient concentration. Formula is designed to be mixed with a precise amount of water to achieve the proper balance of calories, proteins, and electrolytes. Adding it to breast milk instead can result in overly concentrated or diluted feedings, which may be hard on a baby’s kidneys and digestive system.

2. Wasted Breast Milk

If your baby doesn’t finish the bottle, any leftover breast milk must be discarded after 1–2 hours. When formula and breast milk are mixed, it’s not safe to save or refrigerate the remainder for later, which could lead to unnecessary loss of expressed milk—an especially precious resource for many parents.

3. Increased Risk of Contamination

Formula-fed bottles have a higher risk of bacterial growth if not consumed promptly. Mixing breast milk with formula introduces the same spoilage timeline as formula alone. This shortens the safe window for feeding and increases the likelihood of introducing pathogens if proper hygiene isn’t strictly followed.

4. Potential Digestive Upset

Some babies have more sensitive digestive systems and may react differently to mixed feedings compared to receiving breast milk and formula separately. Symptoms can include gassiness, fussiness, or changes in stool consistency. While not dangerous in most cases, this can cause discomfort and make it harder to identify what’s causing a reaction.

5. It Might Affect Your Supply

The more formula you offer in place of nursing or pumping, the less demand there is for your body to make milk. Over time, that can cause your supply to dip—sometimes more than you expected. If maintaining milk production is a goal, you’ll want to be intentional about keeping up regular breastfeeding or pumping sessions, even when supplementing.

Reducing the Impact on Milk Supply

Combination feeding can impact milk supply. The key thing to understand is that breast milk production works on a supply-and-demand system. The more often milk is removed from your breasts (either by your baby or a pump), the more milk your body is signaled to make. So if you start offering formula in place of some feedings, your body may get the message that less milk is needed.

That doesn’t mean your supply will dry up overnight, or even at all. Many parents successfully supplement and continue breastfeeding for months or longer. It just takes a little intention.

Tips to Keep Your Supply Going Strong

1. Don’t Skip Stimulating the Breast
If your baby has a bottle of formula instead of nursing, try to pump around the same time. It doesn’t have to be every single time, but regularly emptying your breasts keeps the milk-making signal going.

2. Prioritize Direct Breastfeeding When You Can
Babies are usually more efficient than pumps, so breastfeeding sessions—especially early on—can help maintain or even increase your supply. If you’re doing a mix of both, try offering the breast first before topping off with formula.

3. Use a Supplemental Nursing System (SNS)
An SNS lets your baby get formula at the breast through a small feeding tube while they nurse. This can be a great way to boost intake without sacrificing breast stimulation. (They can be a bit finicky at first, but some parents love them.)

4. Watch for Signs of a Dip
If your breasts feel consistently less full, your baby is more fussy at the breast, or pumping output drops, you might be seeing a supply dip. It’s not irreversible. Adding back a few extra nursing or pumping sessions can often help rebound your production.

5. Give Yourself Grace
Some drop in supply is normal when supplementing—it’s not a failure, just physiology. If your feeding plan is working for your baby and your sanity, you’re doing it right. Whether you want to protect supply or are ready to wean, you’re still giving your baby love and nourishment either way.

FAQs

1. Can you switch between breast milk and formula during a feeding session?

Yes, you can switch between breast milk and formula in the same feeding session. Offer breast milk first to ensure your baby gets its nutritional benefits, then top off with formula if your baby is still hungry.

2. Will supplementing with formula affect my milk supply?

Supplementing can reduce your milk supply if you nurse or pump less often. To maintain supply, continue breastfeeding or pumping regularly and monitor your milk production.

3. How do I know if my baby needs formula?

Some signs include slow weight gain, signs of hunger after breastfeeding, or a medical recommendation. But many parents also supplement for practical reasons—like returning to work, low supply, or personal choice. It’s okay to do what works for your family.

4. Is it better to breastfeed first or offer formula first?

If you want to keep up your milk supply, breastfeed first. That way your baby is still stimulating the breast, and you can offer formula as a top-up if they’re still hungry.

5. How do I introduce formula for the first time?

Start slow. Try offering a small amount of formula when your baby is calm and not overly hungry. A familiar caregiver, warm bottle, or paced feeding technique can help make the transition smoother.

6. Will my baby get confused between bottle and breast?

Some babies switch easily between bottle and breast, while others may show a preference. Using a slow-flow nipple and paced bottle-feeding can help mimic breastfeeding and reduce the chance of “nipple confusion.”

7. Is it okay to formula-feed at night and breastfeed during the day?

Absolutely. Many parents mix feeding methods based on their routines. Just remember that nighttime feedings do play a big role in maintaining milk supply, so it may help to pump if you’re skipping nighttime nursing.

Whether you are breastfeeding, formula feeding, or supplementing with formula, take solace in the fact that you are providing your baby the nutrition he or she needs to grow and thrive. Feeding time offers special and intimate moments to bond and cuddle with your little one.