You mixed a bottle, your baby fell asleep, and now it has been sitting on the counter for a while. Is it still okay? Here is a clear answer on how long formula can sit out, based on CDC and AAP guidance, with a simple table you can check in a few seconds.
This answer is part of our guide to transitioning from breast milk to formula, which also covers choosing a formula and making it up safely. For more on bottles, breastfeeding and solids, see our baby feeding guides.
How long can formula sit out? The short answer
The CDC advises using prepared infant formula within 2 hours of mixing it, and within 1 hour once your baby starts drinking from the bottle. Throw out whatever is left after a feed. If you won’t use a mixed bottle within 2 hours, put it in the fridge right away and use it within 24 hours.
Why the 1-hour and 2-hour limits matter
Prepared formula is a place where germs can grow, and they grow faster at room temperature than in the fridge. That is why the CDC gives a time limit for mixed formula, rather than leaving it to how the bottle looks or smells.
The clock is shorter once a feed has started. During a feed, germs from your baby’s mouth can get into the bottle. The CDC and the AAP advise using a bottle within 1 hour from the start of the feed and throwing out any formula that is left, instead of saving it for the next feed.
Babies younger than 2 months, babies born before 37 weeks and babies with a weakened immune system are more vulnerable to rare but serious infections from powdered formula. For them, the CDC advises extra preparation steps (see below).
Formula time limits at a glance
| Situation | What the CDC and AAP advise |
|---|---|
| Freshly mixed, baby hasn’t drunk from it yet | Use within 2 hours at room temperature |
| Baby has started the bottle | Use within 1 hour of the start of the feed |
| Formula left in the bottle after a feed | Throw it out; don’t save it in the fridge |
| Mixed bottle not used within 2 hours | Put it in the fridge right away and use within 24 hours |
| Opened liquid concentrate | Cover, refrigerate and use within 48 hours (AAP) |
| Powder and ready-to-feed formula | Follow the storage instructions on the label |
What to do: simple habits that help
- Mix close to feeding time. It is the easiest way to stay inside the 2-hour limit, especially at night.
- Making bottles ahead? Put them in the fridge as soon as they are made, not after they have been sitting out, and use them within 24 hours.
- Note the time. If you often lose track, a quick note on your phone when you mix a bottle or start a feed takes the guesswork out.
- Warming is optional. The CDC says formula doesn’t need to be warmed. If your baby prefers it warm, never use a microwave, because it heats unevenly and can create hot spots that burn.
- Going out? Read the label of the formula you use. Our tips for feeding your baby on the go cover packing bottles for a day out.
- When in doubt, throw it out. If you aren’t sure how long a bottle has been out, a fresh bottle is the safer choice.
Extra steps for young or premature babies
If your baby is younger than 2 months, was born before 37 weeks or has a weakened immune system, the CDC advises boiling the water and waiting about 5 minutes before mixing it with powdered formula, because very hot water (around 158°F/70°C) is needed to kill certain germs. Let the bottle cool before feeding and test the temperature on your wrist. Ask your pediatrician whether ready-to-feed formula is a better choice for your baby. For more everyday tips, see these bottle feeding mistakes to avoid.
Related: how long breast milk can sit out (the CDC room-temperature rules).
When to talk to your doctor
A bottle that sat out a little too long usually isn’t a reason to panic, but contact your pediatrician if your baby:
- is younger than 3 months and has a temperature of 100.4°F (38°C) or higher: call right away
- is feeding poorly, is unusually sleepy or hard to wake, or is very irritable
- has vomiting or diarrhea, or fewer wet diapers than usual
- was born early or has a health condition and you have questions about preparing formula safely
Call 911 if your baby has trouble breathing, turns blue or gray, or is hard to wake.
Frequently asked questions
Can I put leftover formula back in the fridge?
No. The CDC advises throwing out any formula left in the bottle after a feed. Only bottles your baby hasn’t drunk from can go in the fridge, and those should be used within 24 hours.
How long does mixed formula last in the fridge?
The CDC and AAP say prepared formula that is refrigerated right away can be used within 24 hours. The AAP advises against freezing prepared formula.
Does the 2-hour rule start when I mix the bottle or when I warm it?
The CDC counts the 2 hours from when you prepare the formula, and the 1 hour from when the feed begins. Whichever limit comes first applies.
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Sources
- CDC: Infant Formula Preparation and Storage
- HealthyChildren.org (AAP): How long can baby bottles sit out at room temperature?
- HealthyChildren.org (AAP): Fever: When to Call the Pediatrician
This article is for general information only and is not a substitute for medical advice. If you’re worried about your baby, call your pediatrician, or 911 in an emergency.