top of page

Combination Feeding Breastmilk and Formula

Twin Newborn Babies
Twins Can Usually Be Exclusively Breastfed...But Many Twin Parents Like The Flexibility of Combo Feeding

The first thing you need to know about combo feeding is that it is doable, despite what you may have heard. In fact, it is the most common way to breastfeed in the world.

Most sources say you must wait until breastfeeding is established, or about three weeks, before introducing bottles or formula. There is no evidence supporting that rule; we in the lactation field just think it makes sense. Many mothers supplement from the get-go without problems. 

This is probably due to the fact that milk production varies among women; some produce a bountiful supply with little effort, while others struggle to make enough milk, or physically can’t supply enough for their baby’s full needs; and some mothers experience an oversupply of breast milk.

There are many different ways to combo feed, so think about your overall goal for formula amount and breastfeeding amount. It’s important to be consistent about the amount of formula and amount of breastfeeding/pumped milk feeding; the more formula you give, the lower your milk supply will go (unless you pump when you give formula). Remember that you are not alone in wanting or needing to combo feed—one in three babies in the US gets some formula in their first six months.

The most important thing in long-term combination feeding is to keep both bottle feeding and breastfeeding pleasant experiences for the baby. Never force a breast or bottle on the baby. 

Three ways to combo feed

Method One: Exclusive or predominant breastfeeding during the first three weeks

I would recommend doing this, if possible, for the first few weeks to months, then slowly introducing some formula. Like I said, there’s no evidence that this is essential, but it does make sense, and has benefits for your baby in terms of their immune system and development of their digestive system.

The way to do Method One is the following:

Step 1: Once your milk starts coming in, if you have been giving any formula, stop. If your baby is not satisfied with the amount of milk they’re getting while breastfeeding, pump your breasts after feeding, and supplement with the pumped milk. (If your baby is still hungry and you don’t have enough pumped milk, obviously feed them some formula, but increase pumping frequency to help increase your milk production.)

Step 2: After three weeks, if you have a full milk supply (enough to meet your baby’s needs without formula), you can start gradually introducing one bottle of formula a day. Most people choose to do it before they go to bed, so the father, partner, or another family member can give a bottle while the mother sleeps a few extra hours.

After your evening breastfeed, go to bed, while your partner stays up to give the bottle a few hours later. Start with sleeping a maximum of five hours. If your breasts are full but not painfully so, you can stretch it to six hours, but it’s important not to let your breasts get to the painfully full level before feeding/pumping. Full breasts slow down milk production, so it can reduce your supply, especially if you become severely engorged. For a detailed explanation of this process, see this article by Nancy Mohrbacher, IBCLC.

Step 3 (optional): At this point, you may be satisfied with giving one bottle of formula a day, and there is evidence that up to 4 oz of formula a day does not impact overall breastfeeding success. However, you can add more if you wish; as long as the demand (amount and frequency of breast emptying by baby or pump) remains the same, your supply will likely stay the same.* Do this slowly however, and if your breasts feel uncomfortably full, you will have to either breastfeed or pump to reduce the risk of plugged ducts and mastitis.

*Not a guarantee unfortunately; everyone’s body is different, and most moms find a decrease in their supply after they go back to work, even if they are pumping.

Method 2: Combo feeding from birth

The reason this is doable is because your milk supply is very flexible in the first two weeks. Your body is trying to figure out how much to make; do you have twins and need to make double the normal amount? Do you have a large baby or small baby? (Larger babies require more calories than smaller babies; 2.5 oz per pound of body weight is the rule.) Once your body figures this out, if you consistently give the same amount of ounces of formula, your supply will stabilize to whatever amount of milk is coming out on a regular basis.

By introducing a certain amount of formula (you decide how much) and breastfeeding the rest of the time (assuming your baby is good at draining your breasts), you can keep this up indefinitely. (Again, always make sure not to go around with full and uncomfortable breasts; if you’re trying to reduce your supply, just pump enough to be comfortable, not to empty.) 

Method 3: Winging it

This method is the most common throughout the world, and it works. In countries where babies breastfeed for years, mothers supplement when they feel like their babies are still hungry after breastfeeding, and don’t supplement when their baby is satisfied. One caveat is that in these countries, there is typically a culture of breastfeeding, in that almost all mothers breastfeed their babies; in the US, not so much. Social support and tradition have a huge effect on long-term breastfeeding success.

As you can see, you have many options 

Although thinking about long term goals is a good idea, it’s important to be flexible, as your situation can change as your baby grows, or with other life changes. Remember that your baby also has a say in how they are fed, and as they grow older may develop a preference, or even reject the breast or bottle at some point. You may be able to coax them back to your preferred feeding method, or you could graduate to a cup if baby is developmentally ready. 

However you choose to approach combination feeding your baby, you are still every bit as much a successful breastfeeding mother if you and your baby are both thriving!

What Kind of Bottle is Best?

It’s recommended to start with a slow flow newborn size nipple, but be aware that there is no industry standard for what those terms mean, and research shows some of these nipples flow quite fast. I suggest trying several different types, and going with the one your baby seems most comfortable with. More about bottle-feeding here.

More Combo Feeding Resources

Recent Posts

See All


bottom of page