How Long Does Formula Last Once Opened?

In the hazy fog of newborn life, things take on a repetitive motion. Change baby's diaper, give baby a bottle, rock baby to sleep, repeat. So, it's easy to lose track of when you first opened their can of formula, and if it's still good. And trust me: the last thing you want to worry about with a hungry baby on your hands is if their formula is expired, which would make it unsafe to consume. Because even if the expiration date on the can of formula hasn't passed yet, once you open it, the formula inside expires much quicker. All caregivers should know: powdered infant formula is only good one month (or 30 days) after opening the can or by its "Use By" date, whichever is sooner.

Unopened infant formula should be stored inside in a cool and dry place (not the refrigerator), with the lid secured. Never store formula cans in your car or garage, as this could make them spoil thanks to improper temperatures. For help remembering when you first opened it — and therefore when it will go bad — write the date on the lid with a Sharpie.

Ready-to-use formula is a little different. Once the bottle has been opened, it can be stored in the fridge for up to 48 hours before you must throw it out. These precautions protect infants from infection by Cronobacter, a germ that lives in dry foods and water, which could cause sepsis or meningitis in babies.

Precautions must also be taken to make sure infant formula remains safe to drink once it's mixed. Start by pouring safe, clean water in a sanitized bottle, then adding the formula. Follow the manufacturer's instructions to see exactly how much water and formula to mix together to make a bottle (never guess or deviate from the instructions). Once it's prepared and your baby starts drinking from the bottle, they should finish it within one hour, or it should be thrown away.

If the baby did not start feeding from the bottle, the formula you prepared will remain good for up to two hours at room temperature or up to 24 hours in the fridge. However, if they began feeding from the bottle, the baby's saliva will start to mix with the infant formula, potentially causing bacteria to grow and making the formula unsafe. 

Also, discard any formula that shows signs of spoiling, whether in the can or in a prepared bottle. These signs include an odd smell, a different color from normal, or a damaged or dented can. The good news is that most babies in their first year will consume formula long before the 30-day limit. Depending on the size of the formula can, babies will finish an entire can in about a week. Once your baby eats more solids and begins transitioning to whole milk by their first birthday, they may not go through their formula as quickly, so it's crucial to keep track of the day you opened each can.