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How long can formula sit out?

Once formula is mixed, use it within 2 hours if left at room temperature, and within 1 hour once your baby has started feeding from it. After that, throw it out.

If you won't use it right away, put it in the fridge within 2 hours and use within 24 hours.

Strength of evidence

Strong

Based on consistent national public health guidelines (Health Canada, CDC, NHS, AAP) rather than a single study; these are safety recommendations, not RCT-tested time limits.

What the evidence says

Prepared infant formula is not sterile, so bacteria can grow once it's mixed with water. Health Canada advises using a bottle within 2 hours of your baby starting to feed from it, and throwing out any leftovers after that. CDC guidance is similar but slightly more specific: use freshly made formula within 2 hours of mixing it, and within 1 hour once feeding has begun.

If you can't use the formula right away, put it in the fridge within 2 hours of preparing it and use it within 24 hours. Never put it back in the fridge after your baby has already fed from it, since saliva mixed into the bottle encourages bacterial growth.

The UK's NHS gives a slightly longer window, saying unused formula kept at room temperature should be discarded after 2 hours. The safest and simplest approach recommended across guidelines is to make formula fresh for each feed whenever possible.

If your baby was born prematurely, is under 2 months old, or has a weakened immune system, extra caution is recommended since these babies are more vulnerable to infections like Cronobacter.

Sources

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked July 29, 2026

Educational information only. Not medical advice, not a diagnosis, and no doctor-patient relationship is created by using this. Founded Parent has not examined your child and does not know their history, so this may not apply to you. In an emergency, call your local emergency number. What Founded Parent cannot do

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Educational information only. Not medical advice, not a diagnosis, and no doctor-patient relationship is created by using this. Founded Parent has not examined your child and does not know their history, so its answers may not apply to you. Never delay or disregard advice from a qualified health professional because of something you read here. In an emergency, call your local emergency number.