Bottles & Boobs

How long does it take for a baby to adjust to formula change?


Parents change their baby’s formula for many reasons.1 Still, it can be hard to know when a baby formula change is needed and how to go about doing it. 

Good news- babies can often change formulas with no problems. So, if you are looking to change formula for health problems, behavioral concerns or because you want to switch from non-organic to organic baby formula or even from a European brand formula to a US made baby formula, then you will likely be able to do so successfully.

So what’s the best way to switch and how long will it take?

Top reasons to change baby formulas

If you’re already using formula (either alone or as a supplement to breast milk) without any problems, you might wonder why a baby may need to switch formulas or why a parent would choose to make a switch. Most babies will do just fine with a cow’s milk-based formula, although there are a lot of them to choose from.2 But, there are lots of reasons why formula changes happen— to a different cow’s milk-based formula, to a soy-based formula or to a specialized formula.1 Parents may also change formula brands when they can’t get their regular brand or if there has been a baby formula recall of their regular brand due to safety concerns.

Here are some of the reasons a baby formula may be changed: 

1-Baby has an allergy or intolerance to their formula

There are a few reasons that some babies can’t tolerate cow’s milk-based formula. A handful of rare diseases cause babies to have too little of certain enzymes needed to digest milk-based formula.3 The special formulas these babies need are different depending on which disease is causing the problem, so a doctor should always be closely involved in caring for these babies.4

Some babies are allergic to cow’s milk-based formula. Symptoms that could mean your baby is allergic to cow’s milk include:5

Symptoms of allergies right after drinking baby formula include:


Runny nose


Trouble breathing

Symptoms of allergies that happen later after drinking baby formula include:


Bloody poop


Poor growth



A diagnosis of cow’s milk allergy or intolerance can only be made by a healthcare provider. If your baby has any of these symptoms, they should be evaluated and they should be seen right away for dangerous symptoms like trouble breathing. Just like the enzyme diseases above, only a healthcare provider can tell you which formula is best for your baby with a milk allergy or intolerance.

2-Baby requires more formula or calories at each feeding

Infant formula can be expensive. And as infants grow, they need more formula to keep on growing, which means costs grow as well. 

Parents can be overwhelmed by the cost of baby formula. However, if this is the case, it’s important to never add extra water when mixing a baby’s formula to make the powder last longer because this can be very dangerous for babies. Generic or store brands can often be less expensive and are just as safe as brand names because all formula in the US is regulated by the FDA.

Some infants need more calories to grow and develop as expected, so a special formula may be recommended for these babies. This is often the case for premature babies. This is why regular well visits are important for babies so their growth can be closely monitored and a healthcare provider can decide if one of these formulas is necessary for a baby that needs to gain more weight.4

3-Baby is having other symptoms their parents or healthcare provider think may be related to formula

It’s natural to wonder when your baby is fussy, when baby is gassy, or when they are spitting up more than you think is normal if this could be related to their formula. Well, it depends. There are some parents who report improvement in symptoms like this with a new formula and sometimes we don’t really know why that is.6 There are also some parents who change their baby’s formula for something they think is a problem, but is actually normal infant behavior.7

Sometimes a formula change or special formula may be recommended for babies with gastroesophageal reflux disease (GERD)8 or infant colic.4 But how can you tell if your baby’s fussiness is colic? Or if their spitting up is GERD? Or if baby’s poop is normal? You guessed it- only your healthcare provider can give you an answer. This is especially important because some of the symptoms of colic or GERD are the same as those of a milk allergy and many other diseases, so you need a trained professional to evaluate your baby and figure out what’s going on.

Parents often assume the formula is the source of these issues, but that’s not always the case. This is why it’s important to involve your baby’s healthcare provider in a decision about changing formula.

How to change baby formulas

So, how do you go about actually switching baby formula brands or types? 

As we’ve mentioned, you should always talk to your baby’s healthcare provider before changing formula, especially if your baby is having symptoms that concern you. They have advised other parents on how to switch formula dozens of times before and they might have their own tips to share about the process. They will also be able to help you decide which formula is best for your baby

Sometimes you can or should change formulas right away. Other times a more gradual transition is better. But remember, you may not see a change in your baby right away, so it’s not usually a great idea to change formulas too often.

Changing baby formula all at once

An immediate and total formula change may be medically necessary in some cases. For example, if a baby has a severe allergic reaction to milk, their formula should be changed right away since it would be dangerous for them to have a cow’s milk-based formula again.

In other cases, an immediate change may not be medically needed, but may be your only choice. If the store is out of your usual cow’s milk-based formula brand and you had to buy another brand of standard cow’s milk-based formula, it’s OK to transition all at once.9

If you make the switch all at once, be sure to monitor your baby for any new or worsening symptoms. A journal can help keep track of this so you don’t have to remember everything. While changing formulas, especially between brands of the same type of formula, is unlikely to be dangerous, it’s still best to keep an eye out for any changes.10

Changing baby formula gradually 

Some parents and pediatricians prefer changing formulas gradually over a few days to slowly introduce the new formula. This is fine as long as your baby doesn’t have a medical reason for needing a new formula right away. This can also be a good way to change formulas if there is a reason to worry about side effects so the transition is slow and allows more time to watch out for any problems.10

Your baby’s healthcare provider can help you decide exactly how to do this, but the process usually involves making a bottle with a small amount of the new formula and a larger amount of the old formula at first and then, over time, increasing the amount of new formula and decreasing the amount of old formula.10

Just like changing formula immediately, you want to keep an eye on your baby and note any changes with the new formula. Although it’s unlikely, if they have any symptoms that concern you be sure to call your baby’s healthcare provider.

How long does it take to change your baby’s formula?

This is different for different babies and also depends on the significance of the change. Was it a change of one brand to another of the same type of formula? Or a change of formula type? (like milk-based to soy-based) Were the baby’s symptoms mild or severe before the formula change? Was there a true medical problem or just a preference for a different formula?

Some babies may take a full bottle of a new formula right away with no problems.9 Others may take some time to adjust or for their symptoms to resolve, depending on the underlying problem.    

We’ve switched the baby formula- now what?

  • Like we mentioned above, keep an eye on your baby for any new symptoms and whether the symptoms that led to the formula change are getting better. Write this down if you can so you can remember it for your baby’s next medical appointment. Note any changes in pooping, spitting up, fussiness, how much they are eating or anything else you notice. Call the healthcare provider right away if there is a change you are worried about, but otherwise bring your notes to your next visit.
  • Resist the urge to change formula again for a week or two.9 Unless your baby is having a bad reaction to the new formula, give them time to adjust. It might take a few days for the reason you changed their formula to improve and it can be really tough to figure out what’s best if you change formula too often.
  • Don’t throw out all of your old formula. If things don’t work out and your baby is medically able to change back to the previous formula, it’s good to have it on hand.
  • Keep checking in with your baby’s healthcare provider about your progress. They are there to help and care about you and your baby’s wellbeing.

Summary about switching baby formula

There are lots of reasons parents switch their baby’s formula. There may be a medical problem, a parent preference, or a problem getting their usual formula. In general, this is a safe thing to do, but it’s always important to involve your baby’s healthcare provider so you can get the best guidance on how to switch and what formula is best for your baby.

Verified by: Morgan Leafe, MD, MHA


1- Infant feeding patterns in the first 6 months: an assessment in full term infants | Journal of Pediatric Gastroenterology and Nutrition

2- Choosing an infant formula | American Academy of Pediatrics

3- Formula intolerance | Pediatrics in Review

4- Infant formula | American Family Physician

5- Cow’s milk protein allergy in children: a practical guide | Italian Journal of Pediatrics

6- Why babies spit up | American Academy of Pediatrics

7- Formula feeding FAQs: some common concerns | Nemours Kids Health

8- Summary of the 2018 NASPGHAN-ESPGHAN pediatric gastroesophageal reflux clinical practice guideline | North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition

9- Mix and match: Goldilocks formula | Seattle Children’s

10- Your guide to switching baby formula | Forbes

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant's pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

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