There’s no “right” way to feed your baby, and breastfeeding and bottle-feeding aren’t either/or options. In fact, you can do both of these almost from birth or at any point, depending on your own personal situation.

Many families opt to feed their newborns a combination of breast milk and formula for a number of reasons, and these babies grow well and thrive.

If you’re curious about supplementing with formula, we’ve put together a comprehensive primer to help. Read on for why you might want to combo feed and how to offer both breast milk and formula, as well as answers to some common concerns related to supplementing.

What does it mean to supplement with formula?

Supplementing with formula means exactly that — adding formula to your breastfeeding routine, whether you also nurse or pump breast milk to serve in bottles. 

Supplementing with formula is also sometimes referred to as combination or combo feeding. But no matter what you call it, supplementing with formula is pretty easy to establish and most babies take to it well. 

Reasons why you might combo feed

There are a number of reasons why families decide to combo feed (although you also don't need a specific reason for it to be the right choice for your family!). Here are some common scenarios in which families might choose to supplement breastfeeding[1] with formula:

  • You’re going back to work[2]. Although many workplaces are mandated by federal law to allow reasonable unpaid break time for pumping breast milk (check with your company to see what policies are in place), the reality is that it can often be difficult to pump on the job. If you don’t think you’ll be able to take pumping breaks, you’ll likely need to supplement with formula at some stage.
  • You have a low milk supply. There isn’t always a clear-cut reason why some women produce less milk than others. If your pediatrician has determined that your baby isn't getting enough milk during nursing sessions, combo feeding can help bridge the gap.
  • You want to supplement with formula at night. Craving more shut-eye at night is a top reason for supplementing with formula — and who could blame you? Combo feeding can enable your partner or another caregiver to give a formula bottle or two while you catch up on sleep.
  • You need more flexibility during the day. You don’t have to work outside the home to supplement with formula during the day. Breastfeeding is time consuming, and formula bottles can let another caregiver help share feeding duties.
  • It works best for your family. Here’s a little secret about supplementing with formula: you don’t need a specific reason to do it. You can combo feed even if breastfeeding is going well[3]. You can offer baby both breast milk and formla simply because it’s the right choice for your family, period.

How do you feed a baby both formula and breast milk?

Here’s how to begin the process of supplementing with formula:

Getting started with combo feeding[4]

If possible (and sometimes it isn't!), many experts recommend getting a good breastfeeding routine in place before you start offering up formula, which happens roughly in the three- to six- week postpartum period. That way, you’ll have a steady supply of milk.

When you're ready to introduce formula, offer a bottle of formula an hour or two after breastfeeding and then introduce an additional daily bottle-feeding session a few days later.

It can help to make the two feeding experiences feel very similar, which might mean switching sides when formula-feeding (just like at the breast) and burping between sides. You can also hold your babe closely and gaze into her eyes.

Try not to fixate on how much she’s taking from the bottle and instead allow your baby to eat until she's not hungry anymore. She’ll naturally take more when she’s hungry and less when she's not. 

Mixing formula and breast milk in the same bottle 

Whether you’re making formula from powder or concentrate, always prepare it in a separate container according to the manufacturer’s directions first and then add in pumped breast milk. (Ready-to-serve formula can simply be combined with expressed milk).

But never mix breast milk with powder or concentrate instead of water. The wrong amount of water (or no water) can mess with the formulation of vitamins, minerals, electrolytes and other nutrients and sicken your baby.

Although it’s safe to combine your breast milk with formula in one bottle if prepared correctly, lactation experts often recommend giving breast milk and formula separately. That way, none of the breast milk will be wasted if your little one doesn’t finish up the bottle.

Choosing a formula for breastfed babies 

Picking a formula for your baby can seem overwhelming, but your pediatrician is always available to help.

The most common type of formula in the U.S. is cow’s milk-based iron-fortified formula, which comes as a powder, a concentrate or ready-to-serve, and most healthy babies do well with it.

Some formulas are designed specifically for supplementing because they contain lutein, an essential nutrient found in breast milk, as well as prebiotics designed to keep baby’s stool soft, similar to that of exclusively breastfed babies. 

In general, though, don’t think that just because a formula is organic or marketed as "specially formulated," it’s somehow healthier for your little one. Your budget will probably play a role, too. Organic formulas are made of ingredients free of antibiotics, hormones, genetic modification and synthetic fertilizers and pesticides, but they’re also pretty pricey.[5]

Common concerns when combo feeding

Some infants take to bottles easily, though it’s possible yours may hesitate at first.[6] And a new food in your baby’s system might emerge in a very surprising way on the other end!

Here’s more about each issue as well as other common concerns you may encounter when combo feeding:

Will supplementing with formula change my baby’s poop?

Get ready for new output in your baby’s diapers! Exclusively breast-fed babies have poops that are mustard-like in color and texture, sometimes loose or even watery, and seedy, mushy or curdy.

Babies who are formula-fed, at least in part, have stools that are soft but better formed than a breastfed baby's, and they can appear anywhere from pale yellow to yellowish brown, light brown or brownish green. They can have a stronger odor, too.

Does bottle-feeding cause nipple confusion?

Nipple confusion hardly ever happens and this issue is often overblown, as most babies do just fine going back and forth between breast and bottle.

But some do have a little trouble. You can switch the type of nipples you’re using (and the bottles too) to see if there’s a shape or flow level that suits your infant better. Hang in there and know that with a little time, there’s a good chance your baby won’t mind the bottle nipple at all.

Will supplementing with formula impact my milk supply?

It’s possible that supplementing with formula could lessen the milk your body makes, especially if you cut back too quickly on nursing sessions. But a slow and steady approach can keep your supply up, as can pumping when your baby takes a bottle.

Another way to keep your breast milk on an even keel is to nurse first and then offer a supplemental bottle as needed so your breasts are stimulated to keep producing.

What if my baby refuses the bottle?

Indeed, your baby may balk at bottles, especially if you’ve been breastfeeding exclusively. Your infant may also refuse the bottle if you give it, since she’s used to nursing from your breast.

If this is the case, have your partner or another caregiver offer the formula bottle instead. Be sure your infant is hungry enough to try the bottle. You might also start with breast milk and formula in the same bottle so the taste is a bit familiar.

Will supplementing with formula cause extra gas?

Gas happens, of course, even when breastfeeding. But extra gas or fussiness may result when a baby takes in a lot of air when drinking from a bottle. To ease this pain, offer lots of burps during each feeding and change positions so your infant can experience drinking from different angles. 

Combo feeding can seem daunting at first, but soon you and your little one will settle into a new routine. And always check in with your baby’s doctor if you have any questions about your feeding method.