An unopened can of baby formula lasts until the expiration date printed on the container, typically 18 months to 2 years from the date of manufacture. Once you open the can, the clock speeds up considerably: powdered formula should be used within 30 days, and prepared bottles have even shorter windows measured in hours, not days.
Unopened Formula: Check the Expiration Date
Every can of baby formula has an expiration date stamped on the bottom or side. As long as the seal is intact and the can is stored in a cool, dry place, the formula stays safe and nutritionally complete until that date. You don’t need to worry about counting days from purchase. The date does the work for you.
That said, never use formula past its expiration date, even if it looks and smells fine. Formula is carefully calibrated to deliver specific nutrients at specific levels, and those nutrients, particularly vitamins C and B, degrade over time. Expired formula may not make your baby visibly sick, but it may no longer provide adequate nutrition.
After Opening: The 30-Day Rule
Once you pop the lid on a can of powdered formula, use it within 30 days. This is a standard recommendation across major brands and health agencies. After 30 days, exposure to air and moisture accelerates nutrient breakdown and creates conditions where bacteria can grow. Write the date you opened the can on the lid with a marker so you don’t lose track.
Store the opened can with its lid firmly in place, away from heat and humidity. A kitchen counter is fine as long as it’s not near the stove or in direct sunlight. Avoid storing formula near the sink, where splashes and steam can introduce moisture into the powder.
Liquid Formula Has a Shorter Window
Liquid concentrate and ready-to-feed formula follow different rules. Once opened, these need to go straight into the refrigerator (between 35 and 40°F) in their original covered container. Use them within 24 to 48 hours. After that, both bacterial growth and vitamin loss become concerns.
If liquid formula has been left out at room temperature for more than one hour, throw it away. The higher moisture content in liquid formulas makes them far more hospitable to bacteria than dry powder.
Prepared Bottles: A Two-Hour Limit
Once you mix powdered formula with water, the safety window shrinks dramatically. A prepared bottle that hasn’t been fed to your baby can sit at room temperature for up to 2 hours. If you won’t use it within that time, put it in the fridge immediately and use it within 24 hours.
If your baby has already started drinking from the bottle, the timeline gets even tighter: 1 hour, then discard. The moment a baby’s mouth touches the nipple, saliva introduces bacteria into the formula. That bacteria multiplies quickly at room temperature, and refrigerating a partially finished bottle doesn’t make it safe again. This is a hard rule, not a suggestion.
Why These Timelines Matter
The bacterium that poses the greatest risk in powdered formula is one that causes severe meningitis and bloodstream infections in young infants, particularly newborns and premature babies. It survives remarkably well in dry environments, which means it can persist in opened cans of powder and even on scoops and utensils that touch contaminated surfaces. The CDC has documented cases where contaminated feeding equipment transferred the bacteria into formula.
Infections from this organism are rare, but the consequences are serious. Nearly 40% of infants who develop meningitis from it do not survive, and many who do recover face lasting neurological complications. Following proper storage timelines and keeping scoops, bottles, and preparation surfaces clean are the most effective ways to reduce this risk.
How to Tell if Formula Has Gone Bad
Sometimes formula spoils before its expected timeline, especially if storage conditions aren’t ideal. For powdered formula, watch for clumping, changes in texture, a sour or unusual smell, or discoloration (the powder looks darker or off from its original shade). Any of these signs mean you should discard the can.
For liquid formula, the warning signs are separation or curdling, a foul or sour odor, changes in color or consistency, and bloated or damaged packaging. If the container looks swollen or dented in a way that could have compromised the seal, don’t use it regardless of the expiration date.
Quick Reference by Formula Type
- Unopened powder: Good until the printed expiration date (usually 18 months to 2 years from manufacture)
- Opened powder: Use within 30 days, stored with the lid on in a cool, dry spot
- Opened liquid concentrate or ready-to-feed: Refrigerate immediately, use within 24 to 48 hours
- Prepared bottle (untouched): 2 hours at room temperature, or 24 hours in the fridge
- Partially finished bottle: 1 hour from the start of feeding, then discard