Signs Your Baby is Tolerating Their Formula (and When to Switch) Signs Your Baby is Tolerating Their Formula (and When to Switch)

Signs Your Baby is Tolerating Their Formula (and When to Switch)

Erin Moore, MSN, CPNP, IBCLC

This blog was written in paid partnership with Dr. Brown's

Feeding a baby seems like it is straightforward until you actually start! This is especially true when it comes to choosing the right formula for your baby.

Parents are often left wondering: Is my baby tolerating this formula? Is this normal for a baby, or do I need to switch? How much spit-up is a normal amount?

The truth is that some mild digestive concerns can happen when switching formulas. There can be an adjustment period. This can lead to trying multiple different formulas before determining what works best.

Let's walk through the signs your baby is tolerating their formula, the symptoms that show they may require a switch, and how to make decisions without second-guessing yourself.

How to Know if Your Baby is Tolerating Their Formula

A baby can tolerate their formula well and still have some tummy discomfort here and there. Babies' digestive systems are still maturing as they grow. This means that most babies will have mild gas, some spit-up, and a small amount of discomfort from time to time.

Here are signs your baby is tolerating their formula well:

  • They are gaining weight steadily and staying on their growth curve: One of the best indicators of tolerating a formula is how well a baby is growing. This shows your pediatric provider that baby is taking in (and keeping down) enough calories.
  • They are having a normal amount of wet and dirty diapers: This is the number one way to tell if a baby is getting enough milk each day. After the first week of life, babies should have at least 6 wet diapers per day. The number of times a baby poops per day or week varies for each baby. No matter what this number, they should be comfortable pooping without straining.
  • They are content after and in between most feedings. Babies don't need to be happy all of the time, but if you notice a pattern of your baby being upset right after a feed or if they have a lot of discomfort in between feeds, it might be worth considering a new formula.
  • They seem comfortable during feeds. In general, babies should be able to drink a bottle without crying out, back arching, choking, coughing, or sputtering. Discomfort during a feed can be related to a nipple flow rate that is too fast or too slow. If you adjust the nipple flow and they still seem uncomfortable, speak with your baby's pediatric provider.
  • They produce small to moderate amounts of spit up (one or two mouthfuls). Spit-up alone does not mean a formula isn't tolerated. Many babies spit up due to immature digestive systems. If your baby is spitting up small to moderate amounts but is otherwise growing well and comfortable, the formula may still be a good fit.

Signs Your Baby May Not Be Tolerating Their Formula

When your baby's symptoms no longer seem mild, it might be time to speak with your pediatric provider about changing your formula. Here are some signs:

  • Your baby's mood and behavior change.
  • Your baby won't finish bottles and is not getting enough ounces per day.
  • Your baby is not gaining enough weight.
  • Your baby has blood or mucus in their stool.
  • Your baby has new or worsening rashes.
  • You feel the formula is not the right fit for your baby.

How to Choose a New Formula

The first step is talking to your pediatric provider. If your baby was on a standard formula, your pediatric provider might recommend switching to a formula that is "gentle" or "sensitive." Though each formula is different, many have proteins that are broken down to make it easier for your baby’s digestive system.

Good Start® | Dr. Brown's™ Gentle Pro™ formula is a great option for babies with digestive concerns. The formula has 100% whey protein that is easily broken down, which helps promote easy digestion and softer poops.* Another option is the Good Start® | Dr. Brown's™ Soothe Pro™ formula that provides complete nutrition uniquely formulated for sensitive tummies. Formulated with probiotic L.reuteri, Soothe Pro helps reduce fussiness with the first bottle.* The formula provides complete nutrition for babies with sensitive tummies experiencing gas, fussiness, and spit-up. If your baby has severe symptoms or signs of a cow milk protein allergy or intolerance, your pediatric provider will offer suggestions on the right formula for your baby’s needs.

How to Switch to a New Formula

The process of switching from one formula to another truly depends on your baby. There are two approaches: fast and slow.

The fast approach is for babies with severe symptoms or for those babies who are more flexible with change. In this approach, you stop the old formula and offer the new formula at the next bottle.

The slow approach is for babies who might be more sensitive to taste changes. Most babies do well with mixing the current formula and the new formula in the same bottle to help get them used to the new taste. Consider starting with a small amount of the new formula and gradually increasing the amount over several days. Here’s a suggested timeline, though some babies can go faster and others may require an even slower transition over time.

  • Days 1-2: 75% old formula, 25% new formula
  • Days 3-4: 50% old formula, 50% new formula
  • Days 5-6: 25% old formula, 75% new formula
  • Days 7 and on: 100% new formula

Regardless of how you transition your baby's formula, make sure to prepare each formula as stated on the label.

Most babies tolerate their formula just fine. Not every spit-up, episode of gas, or a fussy evening means something is wrong. When you focus on patterns rather than symptoms, the picture becomes much clearer.

Feeding your baby isn't about finding a "perfect" formula, it’s about finding one that supports growth, comfort, and peace of mind for your family.

*Compared to intact protein formulas.

*Study results among parents of fussy infants.

About the Author

Erin Moore, MSN, CPNP, IBCLC, is the founder of Baby Feeding Coach and Fed With Love, a trusted feeding education hub for parents navigating everything from newborn feeding to family meals. With over 15 years of experience in pediatrics, Erin is a pediatric nurse practitioner, lactation counselor, and mom of two boys who understands both the science and the emotional weight of feeding our family.

Erin specializes in helping families feel confident with breastfeeding, formula feeding, starting solids, and toddler eating, without judgment, fear, or internet overwhelm. Her approach is evidence-based, practical, and deeply supportive, meeting parents where they are and helping them choose what works best for their family.

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