How long breast milk lasts
How long pumped milk keeps depends on where it is. The calculator uses the CDC's times:
- Room temperature (77°F or colder): up to 4 hours. Chill it as soon as you can.
- Insulated cooler with frozen ice packs: up to 24 hours when you're traveling.
- Refrigerator: up to 4 days.
- Freezer: about 6 months is best; up to 12 months is acceptable.
The AAP's guidance is close. It adds temperatures: a refrigerator at 39°F or colder (store milk at the back, where the temperature changes least), up to 9 months in a freezer at 0°F or colder, and up to 12 months in a deep freezer at −4°F or colder. For an easy rule, the AAP suggests the "rule of 4s": 4 hours at room temperature, 4 days in the refrigerator.
Thawing and warming
Thawed milk has shorter limits. The CDC says milk thawed in the refrigerator should be used within 24 hours, and once it has been brought to room temperature or warmed, within 2 hours. Never refreeze breast milk after it has thawed.
To thaw frozen milk, the AAP suggests putting it in the refrigerator overnight, holding it under warm running water, or setting it in a container of warm water. Don't microwave breast milk: the AAP says it isn't safe because of the risk of scalding your baby.
In the calculator, thawed milk counts from when you took it out of the freezer. That's earlier than when it finished thawing, so the use-by time it shows errs on the safe side.
Leftover milk
Milk left in a bottle after a feed should be used within 2 hours after your baby finishes, then thrown away. To waste less, store milk in small batches; the AAP suggests 2 to 4 ounces per container, and you can always thaw an extra one if your baby is still hungry.
On the road
For a day trip or a long drive, an insulated cooler with frozen ice packs keeps freshly pumped milk for up to 24 hours. When you arrive, use it, refrigerate it or freeze it. Our baby road trip planner builds feeding stops into your drive.
Babies born early or in the hospital
The AAP notes that hospitals may have their own rules for storing milk for babies who were born early or are in the hospital. If that's you, follow your care team's guidance.