Powdered baby formula is good for up to a month or 30 days after opening.
If you haven't used the baby formula within 30 days or a month it should be thrown out.
However that shouldn't be much of a problem if you're feeding your baby as babies will use a lot of formula and you'll likely use the opened powdered baby formula well within a month.
Within 30 Days Of Opening.
Always use baby formula within 30 days of opening.
Unlike the main expiration date, this reasoning has less to do with the breakdown of nutrition and more to do with the risk of bacteria.
A prepared (but untouched) bottle of formula can be stored in the back of the fridge for 24 hours.
Opened containers of ready-to-feed and liquid concentrate formulas are good for 48 hours.
Powdered formula should be used within one month of opening the can or tub.
How do you know if baby formula has gone bad?
When the formula starts to go bad, you should notice: The smell will have an off aroma. Clumping.
Separation of ingredients in the formula.
The American Academy of Pediatrics (AAP) says that formula out for longer than 1 hour at room temperature should be thrown away.
They also state that formula that has been out for 1 hour or less can safely be stored in the refrigerator.