So, you’ve done the hard work of choosing the best formula for your baby (bravo!)…but that was just the first step in your feeding journey. And now, you’re probably finding that your laundry list of feeding questions continues to grow: Now that you’ve brought those formula canisters home, where do you put them? How do you mix infant formula? Maybe your little one chugged 3 ounces of baby formula, but left an ounce in the bottle. Should you save it for later?

It’s a lot to digest! That’s why we’re here to guide you through all of your questions about storing and preparing baby formula…in a way that goes down easy.

Different Types of Baby Formula

Before we start throwing around “formula” we should define what we’re talking about. 

What is baby formula?

Formula is no monolith! Baby formula comes in three different forms—and each type has its own storage and preparation guidelines. The three types of infant formula are: powdered, concentrate, and ready-to-use. Here’s the scoop on each one…

Differences in Baby Formula

  • Powdered formula: This is the most common and most inexpensive type of baby formula. It comes with a pre-measured scoop you can use to mix the powder with water easily and safely.
  • Concentrate formula: This infant formula comes in liquid form—but it’s not ready to drink. Instead, you mix it with equal parts water. It tends to cost more than powdered baby formula.
  • Ready-to-use formula: Sometimes referred to as RTU baby formula, this is the priciest of the bunch because it’s ready for your baby to drink as is. It often comes in multiple packs starting at two ounces per bottle.

Does it matter what formula I give my baby?

When it comes to choosing the right baby formula, it’s important to know that the Food and Drug Administration (FDA) heavily regulates all commercial infant formulas to ensure they meet safety and nutritional standards. That means that any off-the-shelf formula will give your baby the nutrients they need at this stage of life! However, some babies do have specific dietary needs that might require special formula. If you have concerns about how your baby is handling formula, reach out to your pediatrician. 

How do I know if my baby isn’t agreeing with formula?

Though most babies can switch up formula without incident, some babies do not tolerate formula well. Some signs of a formula intolerance include:

  • Blood or mucus in poop
  • Diarrhea
  • Signs of gas pain (such as pulling legs up and crying)
  • Slow to gain weight
  • Vomiting

If your baby shows the signs of formula intolerance, contact your physician! 

Can babies tell when you change formula?

While most babies are blissfully unaware of any changes you make to their formula type or brand, others are sensitive to changes in their daily meals. For example, you may notice your baby turning away from the bottle or refusing to take it. 

How long do babies need to adjust to a new formula?

It may take your baby several days to adjust to a new formula. To ease the transition, try this gradual introduction: 

If your baby is drinking 4-ounce bottles: 

  • For three days mix 4 ounces of water + 1 scoop of the old formula + 1 scoop of the new formula).
  • On day four, try serving a bottle made entirely of the new formula (4 ounces of water + 2 scoops of new formula).

If your baby is drinking 6-ounce bottles: 

  • For two days, mix their bottles with 6 ounces of water + 2 scoops of the old formula + 1 scoop of the new formula.
  • On day three, mix 6 ounces of water + 1 scoop of old formula + 2 scoops of new formula.
  • On day four, try serving a bottle made entirely of the new formula ( 6 ounces of water + 3 scoops of the new formula).

What to expect when switching baby formulas?

Your little one may experience an uptick in burping and gas for a few days, and you might notice a change in the color of your baby’s poop—all of which is totally normal when switching formulas. (In fact, these are all things you may see again once your tot starts solids!) 

Can I make homemade baby formula?

No! The Food and Drug Administration strongly advises folks not to DIY baby formula. Unlike store-bought baby formula that’s strictly regulated by the FDA, there are no safeguards for homemade infant formula. That means there’s no way to know if homemade formula contains the proper nutrients needed to help your baby grow and thrive. Moreover, homemade baby formula can be dangerous. Babies fed DIY infant formula have been hospitalized for low calcium levels, contamination, and other  inadequacies.

How to Store Baby Formula

Whether opened or not—pre-mixed or powdered—where and how you store your baby formula matters! Here’s how to do it safely. 

Where do I store unopened baby formula?

Store cans of powdered and concentrated formula in a cool, dry area. That means not in the refrigerator and away from a heat source, which includes a hot car. Close contact with heat can weaken the nutrient content of your baby formula. Like powdered baby formula, ready-to-use and concentrated liquid infant formula should be stored in a cool, dry place before being opened.  

Which can of formula should I open first?

Always choose the baby formula that’s closest to expiring. In other words, “use by” dates—typically printed on the packaging—are your friend. Don’t feed your baby infant formula that has passed its “best by” or “use by” date. The formula may not be safe and may have lost some of its nutrients.

How long is an open can of baby formula good for?

Many baby formula manufacturers advise caregivers to use cans of powdered formula within one month of opening. Since the average baby-parent tends to have a lot on their mind, use this pro tip: Keep a permanent marker nearby so you can label each baby formula container with the date you first opened it. Once a month lapses, it’s gotta go.

Concentrated and ready-to-use formulas have a shorter shelf life than their powdered counterparts. Ready-to-use and concentrated baby formula should be refrigerated after they’ve been opened—as long as your tiny feeder hasn’t started sipping on it yet. 

How long is prepared baby formula good for?

Leaving prepared formula out for too long—especially after your little one has already started drinking it—can introduce potentially harmful bacteria into your sweet baby’s bottle. That’s why it’s important to chuck baby formula that’s past its prime. Here’s a quick guide to how long prepared formula is good for….

How long does a bottle of infant formula last for at room temperature?

It’s important to use prepared powdered, concentrated, or ready-to-use baby formula within two hours of preparation, but within one hour from the start of feeding. That means if you make a bottle at 7am and leave it at room temperature, it’s good until 9am. But if your little one starts eating it at 7am, then the bottle is only safe to offer until 8am.

How long does leftover formula stay good in the bottle?

It doesn’t! Bacteria from your baby’s saliva contaminates their formula. The bacteria can grow and render the formula unsafe. That's why it’s best to always discard any baby formula that’s left after a feeding. To avoid tossing out baby formula, place only the amount you believe your baby will eat in the bottle.

How long is prepared formula good for in the fridge?

If you’ve prepared formula that your baby won’t need right away, you can safely store it in the fridge for a short stretch. Depending on the baby formula, it can last anywhere from 24 to 48 hours in the refrigerator.

  • Powdered formula: Use within 24 hours of preparation/refrigeration.
  • Concentrated formula: Use within 48 hours of preparation/refrigeration.
  • Ready-to-use formula: Use within 48 hours of opening.

How long does baby formula last for after you warm it?

After warming the bottle, infant formula is good for one hour. (Though, while many parents prefer to warm their baby formula before serving, it’s actually not necessary!) To warm your baby’s formula safely, run the formula-filled bottle under warm water or use a bottle warmer. Be sure to place a couple drops of formula on the back of your hand to gauge how hot it is. Never microwave baby formula, which can result in dangerous “hot spots” that can burn your baby’s mouth.

How long does baby formula last in the freezer?

It doesn’t! While it’s okay and totally safe to freeze breastmilk, infant formula should never be placed in a freezer because the icy temps can cause the formula’s components to separate.

Can I prepare baby formula ahead of time?

Some parents and caregivers make bottles as often as Baby eats, and others prefer making baby formula ahead of schedule. If your baby gets hungry every three hours and usually takes 6 ounces of formula at each feeding, you may consider preparing eight bottles of formula for a 24-hour period. Of course, making fresh bottles at each feeding time is perfectly okay, too! But be warned: If your little one doesn’t guzzle the whole bottle, you’ll need to discard whatever’s left over after an hour.

How to Prepare Baby Formula

Before showcasing your mixology skills, thoroughly wash your hands with soap and warm water—and ensure your baby bottle and accessories are clean. (For more detailed instructions, take a look at the CDC’s guide cleaning and sanitizing infant feeding items.)

Unless your baby’s pediatrician instructs otherwise, follow the instructions on the back of the infant formula can and use the scoop provided. You can trust that your chosen baby formula is designed to deliver the just-right ratio of fluid and nutrients for your baby’s growth and development. Please don’t try to wing it! Incorrectly mixing infant formula can rob your precious babe of the nutrition they need and give them too much or too little fluids…potentially causing dehydration or kidney troubles. 

How do you make a bottle of baby formula?

A standard powdered formula recipe calls for 2 ounces of water for every one scoop of formula. To prepare 4 ounces of baby formula for your sweetie, add 4 ounces of water and mix two level scoops of formula. Always measure the water first…and then add the powder. (That said, always read the directions on your specific can of powdered baby formula.)

  • Powdered formula recipes use a 2:1 ratio of baby formula to water. For a 4-ounce bottle, mix 4 ounces of water with two scoops of formula.
  • Concentrate formula must be mixed with water at a 1:1 ratio. So, if you’re preparing a 4-ounce bottle of formula, you’d blend 2 ounces of formula with 2 ounces of water.
  • Ready-to-use formula is just like it sounds—it’s ready to use and doesn’t need to be mixed…so step away from the faucet!

Can I use tap water to make baby formula?

Yes…unless there’s a known contamination of your local water source. It’s totally safe to use fluoridated water for preparing infant formula. But if your baby is only consuming baby formula mixed with fluoridated water, there may be an increased chance for mild dental fluorosis (aka: white spots on their teeth). To dampen the risk, you can occasionally use low-fluoride bottled water, like distilled or purified bottled water, to mix your infant formula.

How do you make baby formula for preemies?

If your baby was born prematurely or has a weakened immune system, it’s a good idea to contact your baby’s pediatrician to find out if you need to take any extra precautions in preparing your little one’s formula. In some cases, ready-to-use formula will be advised over powdered formula. Other times, your child’s pediatrician may suggest you boil the water used with formula to kill any microbes. (Boil water, let it cool for about 5 minutes, add to a clean bottle, then add the powdered formula. Make sure the baby formula is at body temperature before feeding.)

Get more baby feeding tips:


  • The American Academy of Pediatrics: Forms of Baby Formula: Powder, Concentrate & Ready-to-Feed
  • U.S. Food & Drug Administration: Infant Formula Safety Dos and Don’ts
  • Minnesota Department of Health: Changing Formulas, June 2022
  • Centers for Disease Control and Prevention: How to Prepare and Store Powdered Infant Formula
  • Centers for Disease Control and Prevention: Infant Formula Preparation and Storage
  • Centers for Disease Control and Prevention: How to Clean, Sanitize, and Store Infant Feeding Items
  • Centers for Disease Control and Prevention: Community Water Fluoridation, Infant Formula
  • The American Academy of Pediatrics: How to Safely Prepare Formula With Water

About Gabrielle McPherson

Gabrielle McPherson, MS, RDN, LDN is registered dietitian in Missouri who specializes in community and pediatric nutrition. Gaby is passionate about encouraging families to eat well in simple, practical ways that are realistic...and delicious! When not working, Gaby loves cooking, baking, and making messes and memories with her sous-chef/preschooler Charlotte.

View more posts tagged, feeding

Have questions about a Happiest Baby product? Our consultants would be happy to help! Submit your questions here.

Disclaimer: The information on our site is NOT medical advice for any specific person or condition. It is only meant as general information. If you have any medical questions and concerns about your child or yourself, please contact your health provider.