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When we discuss choices around feeding our babies, the discussion tends to be very binary — either breast milk or formula. The reality, though, is that the vast majority of parents end up using some combination of these options, either in parallel (using both formula and breast milk at the same time) or in sequence (starting with breast milk, eventually switching to formula).
This is often called “supplementing with formula,” but I prefer the term “combo feeding,” which I think better captures the overall strategy for many parents.
People choose to combine breast milk and formula for many reasons. One is supply issues; sometimes, there just is not enough breast milk. This can be true from the beginning, or it may arise later when someone returns to work and is pumping. Sometimes, parents plan to combo-feed from the beginning, so two parents can be more involved with the feeding journey. You may choose to switch from breast milk to formula because you don’t like breastfeeding or because it’s painful. When mothers return to work, they may decide that pumping is not working and will gradually switch to formula.
Regardless of the reason, combo feeding can be difficult for parents for at least two reasons. One is that, especially when people had expected to exclusively breastfeed, they often feel bad or like they have failed when they use formula. The second issue is that when we have more choices, there are also more logistics — figuring out how formula bottles and pumping/feeding schedules can fit together.
How common is combo feeding?
In 2024, I partnered with Bobbie and Willow to survey parents about their infant feeding journeys. We surveyed 1,899 women about their experiences. When we asked about their expectations for feeding, only 11% said they planned to combine nursing, pumping, and formula. In the end, though, 87% worked with some combined feeding plan.
In our survey, parents reported very limited support with combo feeding, and that leaves both of these issues unanswered. Having those answers is the key to having a better and more confident plan.
How much breast milk is “enough”?
Most new parents hear extensively about the benefits of breastfeeding — better health, both short and long term, better cognitive development, etc. However, many of these claimed benefits are not supported by the best data. There are some benefits to breastfeeding, but they are much smaller than most people think.
The benefits best supported in the data are a reduced risk of gastrointestinal illness early on, a small reduction in the early risk of eczema, and possibly a reduction in ear infections. There are also benefits for NICU babies in reducing the risk of a serious digestive issue. These are all short-term impacts and, while real, are smaller and more limited than many people think. They are concentrated in the first months of life.
This is important to say first because the questions on combo feeding — how much breast milk is enough — are predicated on the view that “breast is best.” Once we are clearer on what that really means, I think this question becomes less important. My sense is people are looking for an answer like: If you do 51% breast milk, you get all the benefits. But the reality is that there isn’t some magic threshold, and, again, the benefits are small even if you switch from 0% breast milk to 100% breast milk.
To the extent there is value in breast milk, it is concentrated in the first months of life, so this question becomes even less salient as babies get older.
The upshot: Although this question is the first that comes to the mind of most parents, it probably should not be a large part of the calculus. The logistics around the best approach to feeding for your family should be more central.
How to make a combo feeding plan
If you are choosing to combo feed, your life will be easier if you make a deliberate plan about it up front. Exactly what this looks like will depend on why you’re choosing this, but here are some examples.
You are planning to combo feed from the beginning. For some people, their plan at the start is to mix formula and breast milk. If you are doing this, you should plan which time of day you will use formula, since your supply will adjust to this.
Your supply is low, so you’re supplementing with formula. If you’re hoping to increase your supply going forward, the right approach here is usually to nurse first and then provide a bottle after each feed to “top off” the baby. Sometimes, people are recommended to pump after nursing in this situation to increase supply; this depends on your goals. Over time, as supply increases, the bottle may become less necessary.
You are planning for one of the late-night feeds to be formula. Combine this plan with your overall nighttime routine and pick a time. Decide if you will pump during the feed to keep up your supply or not.
You are planning to ramp down breastfeeding as you return to work. Decide how quickly you want to do this and make a plan for whether you’ll mix milk and formula together as you switch over, or make the switch all at once.
Your situation may be different, but I promise you’ll be happier with this if you think about it before you implement it.
Frequently Asked Questions
Let’s end here with a few FAQs that can help your planning.
Can I mix pumped breast milk and formula in the same bottle?
Definitely yes, and one ounce of formula can be substituted for each ounce of breast milk, so it’s easy to do. You should make the formula with water, and then add it to breast milk at a 1:1 ratio (do not make formula with breast milk as the liquid). One main reason people mix the two is to get their child used to the taste of formula. It doesn’t taste the same as breast milk, and sometimes babies reject it (sometimes they love it!). If you slowly increase the amount of formula in the bottle, this can ease them into the new taste.
If I switch some of my feeds to formula and pump less, will I lose my supply?
Yes, to some extent, but this varies a lot across people. Some people can maintain a high level of supply even if they are only nursing in the morning and at night, while others find that this completely eliminates their milk supply. Unfortunately, the only way to learn about this is to try; although if you find your supply is declining quickly, you can reintroduce pumping or nursing sessions to increase it again.
If I start by combo feeding, is there a chance I will end up exclusively breastfeeding?
Absolutely. Many people combo feed early on, as their milk supply is getting established. And many of these people ultimately are able to exclusively breastfeed once their supply increases. If you are hoping for this, the main advice is to start all feeding sessions by nursing, which gives your body the cue to produce more milk.
Will my baby develop a preference for the bottle?
It is possible, yes, although it is also possible that they will not like the bottle, which can present its own challenges. Having said this, most babies are able to combine these modes of eating. One thing that can help is using bottles with slow-flow nipples, so they deliver milk at a pace similar to breastfeeding.
How can I make sure my baby is getting the same amount of milk from a bottle as they do when they breastfeed?
Short answer: It’s impossible to be sure these are equivalent since we generally do not have a precise estimate of what babies take in while breastfeeding. In most cases, your baby’s cues will tell you when they are done eating with either nursing or formula, and that is more important than the exact amount. Assuming a baby is gaining weight, you don’t have to monitor this precisely.
Does formula make babies sleep longer at night? Should I do the formula bottles at night and breastfeed during the day?
Formula is more difficult to digest than breast milk; as a result, exclusively breastfed babies do wake up more in the night than formula-fed babies. This may argue — although, again, make your own plan — for using formula at night when you are hoping for more sleep.
Do I still need to give my baby vitamin D drops?
Vitamin D drops are recommended as long as you are doing some breastfeeding. To be completely honest, the dosing of these isn’t very precise. It is possible to overdose on Vitamin D but only at extremely high levels. In order to avoid having too little vitamin D (which is also very rare), the recommendation is to use these through the first year, even if you are using some formula.
How can I make sure my milk supply stays high without pumping constantly? And can combo feeding work without pumping?
This depends on your goals. In establishing your supply initially, pumping is likely to be helpful if you are using formula from the start. This gives you a baseline supply, and it’s easier to dial down the supply than dial it up.
As time goes on, breast milk supply responds to demand. If you stop pumping, your body will produce less milk and will adapt the time of day you produce milk to when you are nursing. This may work fine, but it’s worth thinking through if you (say) plan to feed differently on weekdays and weekends. If you are hoping to exclusively breastfeed when you’re home on Saturday, for example, you’ll likely need to pump at work during the week to keep the supply up. This isn’t the same for everyone; some people retain milk supply differently than others, so supply-adapts-to-demand is a good general rule.
The bottom line
- While many people might not plan from the beginning to combo feed, many ultimately end up doing so.
- There are some benefits to breast milk, but they are small and concentrated in the first months of life, so there’s no magic “enough” threshold. Your family’s feeding logistics matter far more than hitting a specific percentage of breast milk.
- Making combo feeding work smoothly mostly comes down to deciding your goals and planning ahead — choosing when to use formula, how (or whether) to keep up your milk supply, and how to adjust feeding as your needs change.
A correction was made on December 10th, 2025: An earlier version of this article incorrectly stated that Vitamin D was water-soluble.
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Thank you so much for talking about this! I wound up combo feeding with my first (although that wasn’t the plan) and absolutely loved it and decided to do the same with my second, but there isn’t as much guidance or advice there. Your work on accurately assessing the benefits of breastmilk helped alleviate the guilt and helped me advocate for myself!
Vitamin D is fat soluble, not water soluble, so it is possible to dose too high!
Thanks for your comment! This has been updated.
Yes, I was going to comment that too. The fat soluble vitamins are A,D,E and K for reference. They can accumulate and are not easily excreted in urine.