How Long Does It Take a Baby to Adjust to Formula Change?

Most babies adjust to a new formula within 3-5 days, however other may take up to six weeks. You child’s new digestive system and the type of formula cause fluctuations in the time it takes to adjust. Always speak with your pediatrician before switching formulas. 

Maybe you suspect that your little one is lactose intolerant, or they seem to be experiencing acid reflux. Regardless of the reason, you recently changed the type of formula you give your baby. 

You probably wonder how long it will take your little one to adjust to this new formula. If your child was previously experiencing some gut upset that inspired the switch, this is a natural question. 

I wish I could give you a magic number for how long it will take your baby to adjust when switching formula! The most optimistic timeframe to expect is 3-5 days, while the longest timeframe was six weeks. 

Due to this range, try giving your child at least two weeks to adjust to a new formula is a good rule of thumb. 

Asking your child’s pediatrician for their input is always a good idea as well. They should be able to provide more specific expectations depending on your child’s specific situation.

Adjusting to Changes in Formula

The good news is that your little one should fully adjust to their new formula in about two weeks! The bad news is that two weeks can feel like a lifetime if your little one is unhappy. 

For an easier transition to a new baby formula, follow the steps below. 

Formula Family Trees

While you are probably familiar with the concept of a family tree, you may not know that baby formulas belong to a “family tree.” The first consideration when switching formulas is determining what family tree your child’s current formula belongs to. 

It’s important to know this because it can gauge how smooth (or difficult) your child’s transition will be. 

If the new formula is part of the same family tree as your current formula, then the change should be pretty straightforward.

If your baby’s current formula and the new formula are in different family trees, then it will be a bigger adjustment for your child’s digestive system. 

This doesn’t mean a transition between formula family trees is impossible! It just means that you and your little one may have to put more effort into the change to make it successful.

The Bovine-Based Family Tree

Let’s start with the largest of the formula family trees. This formula family is likely the type of formula you currently feed your child (if health issues aren’t a concern). 

Infant formulas within the bovine-based family tree consist of a cow’s milk base. The term “bovine” is a fancy term that refers to wild and domestic cattle, like cows (i.e., bovine droppings vs. cow pies). 

Note that infant formula in the bovine-based family mimics the dairy proteins in cow’s milk but is still very different than cow’s milk.

Similac and Good Start infant formula are examples of the types of formulas in the bovine-based formula family tree. 

The Goat-Based Family Tree

In this formula family tree, you will find baby formulas designed to mimic goat’s milk.

The popularity of goat-based formula is nowhere near cow’s milk-based formula but has gained popularity for a few reasons. It tastes more like breastmilk and is easier to digest.

Goat-based formulas can also be a good option for children that have eczema. A few popular goat-based infant formulas are Kabrita USA, Holle Goat, and Sammy’s Milk. 

The Low-Lactose Family Tree

These infant formulas are designed with part of the digestive process already completed for your little one, which means less work for their digestive system.

Formulas that are a member of the low-lactose formula family tree is likely to have words like “gentle” or “sensitive” in their name (i.e., Similac Sensitive). 

The Soy-Based Family Tree

Infant formulas in this family tree are made out of soybeans and should have the word “soy” on the packaging.

If you think your child is either lactose intolerant or is allergic to the cow-milk protein, soy may be a good option because it does not contain any lactose or dairy. 

The American Academy of Pediatrics (AAP) also recommends soy-based formulas for infants with galactosemia.

However, the AAP does not recommend soy formulas if your infant was born prematurely and with low birth weight or to help prevent colic. Prosobee, Allsoy, and Isomil are popular soy-based formulas. 

Hypoallergenic Formula Family Tree

This is the most expensive of the formula family trees. These formulas are lactose-free and generally used as a last resort for lactose-intolerant babies, those with severe allergies, or those who have severe colic with no relief from other formulas. 

Your pediatrician would likely initiate this transition. There is no need to select a hypoallergenic formula if it is not necessary.

These formulas are gentler on the stomach than those in the low-lactose formula family tree and require minimal digestion. Pregestimen, Nutrimigen, and Alimentum are popular hypoallergenic formulas. 

Transition Slowly

Now that you determined whether the formula you are currently using and the formula you are switching to is related or not, you are ready for a transition plan.

The transition plan will vary depending on how difficult you feel the switch will be for your child (trust those motherly instincts).

If the formulas are members of different family trees (i.e., bovine-based vs. low-lactose), it is suggested to transition slowly using one of the methods below. 

Same Scoop-to-Water Ratio

Check to see if the current formula and the new formula have the same scoop-to-water ratio.

If the formulas have the same ratio, a great way to start the first 1-2 days is with 75% of the current formula with 25% new formula in each bottle.

The next two days (day 3-4), try filling the bottle with 50% current formula and 50% new formula.

On day 5 and 6, mix 25% of the current formula with 75% of the new formula.

Then, officially transition to 100% of the new formula by day 7.

Feel free to slow it down by repeating any step for more than one day. 

Different Scoop-to-Water Ratio

If the old and new infant formula you are switching to do not have the same scoop-to-water ratio, don’t worry.

You can use the same percentage steps for each day outlined above. However, prepare each formula in a separate bottle before combining them into one bottle.

This way, you will ensure that you get the correct formula-to-water ratio for each formula.

If this seems a little complicated, you can avoid combining the current formula and new formula into the same bottle altogether.

Day 1: Offer your child one bottle filled with the new formula. Then, offer the rest of the bottles for that day filled with the formula they are used to.

Day 2: Give your child two bottles with the new formula. Then, the rest of the bottles will still contain the old formula.

Day 3: Introduce a third bottle with the new formula and the rest with the familiar formula. By adding one additional bottle of new formula each day, you can slowly work towards a complete transition. 

Make Observations

You have made it to step three and probably think that you would have more time to sleep if one-step solutions for babies existed.

Now that your infant has hopefully made a successful transition to the new formula, you can sit back and relax (as much as you ever can with a little one). 

Monitor for Intolerance

Now you will want to monitor for any red-flag symptoms (hives, thick or runny poop, blood, or excessive gas) that might pop up and keep a log so you can let your pediatrician know. 

While you monitor for signs of intolerance, remember that one bad poop should not sound an alarm.

Minor symptoms of acid reflux, gas, loose stools and fussiness are the digestive system’s normal reaction to something new.

Minor symptoms should subside as your child adjusts but should still be reported to your child’s pediatrician. 

Monitor for Appropriate Weight Gain

During this time, observe your little one’s feeding habits with the new formula and make sure that they are still gaining or maintaining their weight.

If your child does not like the new formula’s taste and refuses to drink it, you will likely need to make a change. 

Work Together With Your Pediatrician or Lactation Consultant

Expect it to take about two weeks for your baby to adjust to a formula change. Two weeks might seem like a long time, especially if your child has only been alive for eight.

It is a small sacrifice to make in the long run, especially if you see improvements with the new formula.

You can help them adjust to the formula change by transitioning to the new formula slowly.

Just as you learn each day, the most important thing is patience and communicating with your pediatrician.