An opened can of powdered infant formula lasts about one month. Most manufacturers set this as a firm cutoff, and the CDC recommends the same timeline. But “how long does a can of formula last” has several answers depending on whether you’re asking about the sealed can on your shelf, the opened powder in your pantry, liquid formula in the fridge, or a prepared bottle on the counter.
Opened Powdered Formula: The 30-Day Rule
Once you pop the lid on a can of powdered formula, you have roughly 30 days to use it. Write the date on the lid the day you open it so you’re not guessing three weeks later. After a month, the powder starts losing nutritional quality, and the risk of bacterial contamination increases with each additional day of exposure to air and moisture.
Store the opened can in a cool, dry place with the lid sealed tightly. The refrigerator is not the right spot. The humidity inside a fridge can cause the powder to clump and absorb moisture, which actually creates a better environment for bacteria to grow. A kitchen cabinet away from the stove or dishwasher is ideal.
Unopened Cans and Expiration Dates
An unopened can of formula stays good until the date printed on the packaging, which is typically 12 to 18 months from the manufacture date. There are two types of dates you might see. An expiration date marks the last day the formula should be used at all, because safety becomes a concern beyond that point. A “use by” date is slightly different: it marks when the formula may start losing nutrients, particularly vitamins that degrade over time. Either way, don’t use formula past whatever date is printed on the can.
Store unopened cans at room temperature. Extreme heat, like a garage in summer, can accelerate nutrient breakdown even before the printed date.
Liquid Formula Has a Much Shorter Window
Liquid concentrate and ready-to-feed formula follow completely different rules once opened. These need to go in the refrigerator immediately, stored at 35 to 40°F, and used within 24 to 48 hours. Keep the liquid in its original container with the cap on. After two days, nutrients like vitamin C and B vitamins begin to break down, and bacterial growth becomes a real concern even at fridge temperatures.
If liquid formula has been left out at room temperature, discard it after one hour. The higher moisture and nutrient content in liquid formula makes it a much more hospitable environment for bacteria than dry powder.
Prepared Bottles: A One-Hour Counter Limit
Once you mix powdered formula with water and pour it into a bottle, the clock starts ticking fast. A prepared bottle left at room temperature should be discarded after one hour. If you’ve made a bottle but your baby isn’t ready to eat yet, you can store it in the refrigerator and use it within 24 hours.
The timeline gets even shorter once your baby starts drinking. A bottle that has touched your baby’s mouth should be finished or thrown out within one hour of the feeding starting. Saliva introduces bacteria into the formula, and that warm, nutrient-rich liquid is an ideal growth medium. Reheating a partially finished bottle does not make it safe again.
Why These Timelines Matter
Powdered infant formula is not sterile. A bacterium called Cronobacter can survive in dry environments like formula powder, and while it’s harmless to most people, it can be life-threatening for infants younger than two months, babies born prematurely, and those with weakened immune systems. Public health investigations have linked most infant infections to contamination that happens during formula preparation and storage, not at the factory.
This is why the storage rules exist. Every time you scoop powder from an open can, you introduce air, moisture, and whatever is on the scoop or your hands. Over 30 days, these small exposures add up. Beyond that window, the risk of enough bacterial growth to cause illness climbs in a way that isn’t worth the savings of stretching a can a few extra days.
Quick Reference by Formula Type
- Unopened can (any type): safe until the printed expiration or use-by date, stored at room temperature
- Opened powdered formula: use within 30 days, stored in a cool dry place with the lid sealed
- Opened liquid concentrate or ready-to-feed: refrigerate immediately, use within 48 hours
- Prepared bottle (not yet fed): 1 hour at room temperature, or up to 24 hours in the fridge
- Bottle baby has started drinking: finish or discard within 1 hour
If you’re ever unsure whether formula is still good, the safest move is to toss it. A half-used can that’s been open for six weeks or a bottle that sat on the nightstand overnight isn’t worth the risk, even if it looks and smells fine. Bacterial contamination at dangerous levels doesn’t change the appearance or smell of formula.