How to prepare formula: A step-by-step guide to safely making a bottle

When you’re a parent ready to shift from breast to bottle or a caregiver new to infant feeding, it’s normal to have questions about how to prepare formula. Which goes first, the water or the formula? Should the water be cool or warm? And what do you do if there’s formula left over?

“Providing an infant with the proper nutrition is critical to their development and growing along a healthy curve,” says Emily Silver, a Charlestown, Massachusetts, family nurse practitioner, lactation consultant and co-founder of parent support platform NAPS. “In general, it’s good practice to get familiar with your own formula and carefully read its guidelines for preparation and safe storage, as different brands can vary.”

But don’t worry. Though you should always refer to the instructions on the formula label, there is a standard procedure for safely preparing a bottle of baby formula. Here’s how.

1. Check the formula first

There are a few things the Centers for Disease Control and Prevention (CDC) says to check before preparing a bottle:

Expiration date

“Expired formula should not be used since critical ingredients may be past their prime, leaving the baby at risk of a nutritional deficiency,” says Dr. Natasha Burgert, a Kansas-based pediatrician, and spokesperson for Philips Avent and the American Academy of Pediatrics (AAP).

Condition of the container

Make sure any new container of formula is sealed. A rusted or unsealed container could mean the contents are contaminated, making the formula unhealthy for the baby.

The label

Babies and toddlers have different nutritional needs. The CDC recommends double-checking that your formula label matches the infant’s age.

It’s also important to be aware of recent safety recalls to ensure you’re feeding the baby a safe formula, says Silver.

2. Wash your hands

It’s vital to wash your hands before preparing a baby’s bottle, says Silver.

The CDC offers these guidelines for handwashing before food preparation:

Wet your hands
Lather up with soap for 20 seconds, making sure to rub between your fingers and around your nails.
Rinse your hands under clean running water.
Air dry your hands or pat them dry with a clean towel.

3. Clean the bottle

Never mix formula in a bottle that hasn’t been recently washed. “Bottles themselves can be contaminated with bacteria, so proper cleaning and storage is best practice,” says Burgert.

Sanitizing (for new bottles and certain infants)

If you’ve taken the bottle out of the package for the first time, you should sanitize it. The CDC also recommends daily bottle sanitizing for babies born prematurely, younger than 2 months, and with compromised immune systems.

Here are three bottle sanitizing methods suggested by Burgert:

Boil the bottle and its parts for 5 minutes, then allow to air-dry until cool.
Run dishwasher-safe bottles and their parts through a dishwasher’s “Sanitize” setting.
Use a countertop bottle sterilizer such as Philips Avent Premium Sterilizer or Baby Brezza One Step™ Baby Bottle Sterilizer Dryer.

Washing (for daily bottle cleaning)

“Daily maintenance should include washing parts with hot soapy water, steaming or dishwashing,” says Silver.

To handwash a bottle before preparing formula, follow these steps:

Take the bottle apart so you can wash each part separately.
Rinse each piece under clean running water.
Place the parts in a clean basin of hot, soapy water.
Scrub each item with a clean bottle brush.
Rinse everything again, then place on a clean towel or paper towel to dry.

4. Measure and add the water

Always add the water to the bottle before adding liquid-concentrate or powdered formula. This is critical to measuring and mixing the formula correctly.

“Ingredients need to be rehydrated correctly so a dangerous imbalance is not created,” says Burgert. Too little water causes digestion issues, she explains, while too much water can dilute calories and impede infant growth.

Here’s how to prepare the water:

Read. The instructions on the label will tell you how much water to use based on the bottle size.
Measure. Use any water — tap, filtered, or bottled — as long as it is clean and safe. The AAP recommends tap water, says Silver, because it has fluoride that is good for healthy teeth and gums. Burgert adds that tap water is nice because it can be adjusted to the baby’s preferred temperature.
Pour. Once measured, put the water into the bottle.

5. Measure and mix in the formula

Read (again!). The recent formula shortage means you’re more likely to find unfamiliar brands at the grocery store. Formula concentration can vary, so Burgert suggests paying careful attention to the powder-to-water ratio on the label.
Add. Use the provided scoop (if available) to place the correct amount of formula into the bottle.
Mix. Screw the bottle cap on and shake well.

6. Safely warm the bottle (optional)

It’s perfectly safe for babies to drink room temperature or even cold formula, says Burgert. She adds, “Getting your baby used to drinking room temperature formula can make bottles on-the-go much easier.”

If you want to warm the bottle anyway, do not use the microwave. Silver says this can produce dangerous “hot spots” that will burn the baby’s mouth.

Here’s how she recommends warming a bottle:

Fill a mug or deep bowl with hot water.
Immerse the bottle in the water and allow it to sit for about 5 minutes.
Remove the bottle from the water.
Test the liquid’s temperature with a clean fingertip or by putting a drop of milk on the back of your hand.

7. Use immediately or store properly

Once the formula is mixed, give it to the baby or refrigerate it immediately. You should discard any prepared formula that isn’t used within 24 hours.

Some caregivers find it helpful to prepare a few bottles or a lidded container of formula all at once. To do that, label the container with the date and time and be prepared to discard any leftovers after 24 hours.

Frequently asked questions about how to prepare formula

Can you make bottles of formula in advance?

Silver says you can mix most formulas in advance if you refrigerate and use them within 24 hours.

“If parents are using a lot of formula, they can make a batch, similar to a pitcher of lemonade, and keep it prepared in the fridge for easy access,” she says.

Do you have to boil water for formula?

Not necessarily, says Silver. “Commonly, packaging on formula reads to use filtered or boiled water. This is because it’s a global recommendation,” she explains. But if your tap water is clean, it might not need to be boiled. Contact your health department to find out if your local tap water is safe for infant formula.