How breast milk storage works
These limits come from the CDC's guidance on the Proper Storage and Preparation of Breast Milk. The safe window depends on two things: what state the milk is in (freshly expressed, previously frozen and thawed, or leftover from a feeding) and where you are keeping it (room temperature, the refrigerator, or the freezer).
Two rules matter most. First, once milk has been frozen and thawed, you should never refreeze it - use it within 24 hours in the fridge or 1 to 2 hours at room temperature. Second, once a baby has started drinking from a bottle, that leftover milk should be used within 2 hours and then discarded, no matter where it has been.
Tips for storing and thawing
Store milk in the back of the fridge or freezer, not in the door, so it stays at a steady temperature. Freeze in small batches to cut down on waste, label each container with the date, and use the oldest milk first. Thaw in the fridge, in warm water, or under lukewarm running water - never in a microwave, which creates hot spots and can damage the milk.
Frequently asked questions
How long does breast milk last at room temperature?
The CDC recommends using freshly expressed breast milk within 4 hours at room temperature (up to 77F / 25C). Milk that was previously frozen and thawed should be used within 1 to 2 hours at room temperature. Leftover milk from a bottle the baby has started drinking should be used within 2 hours, then discarded.
How long does breast milk last in the fridge?
Per CDC guidance, freshly expressed milk keeps for up to 4 days in the refrigerator at about 40F (4C). Previously frozen milk that has thawed should be used within 1 day (24 hours). Store milk in the back of the fridge rather than the door, where the temperature is more stable.
How long does breast milk last in the freezer?
The CDC says freshly expressed milk is best used within 6 months in the freezer (0F / -18C) and is acceptable up to 12 months. Freeze in small batches toward the back of the freezer and leave room for the milk to expand.
Can I refreeze thawed breast milk?
No. The CDC advises that breast milk which has been frozen and then thawed should never be refrozen. Once thawed, use it within the thawed time limits - within 24 hours in the refrigerator or 1 to 2 hours at room temperature.
How long is leftover milk from a bottle good for?
Once a baby has started feeding from a bottle, the CDC recommends using the leftover milk within 2 hours and then discarding it, because bacteria from the baby's mouth can get into the milk during feeding.
How should I thaw frozen breast milk?
Thaw the oldest milk first, either overnight in the refrigerator, in a container of warm water, or under lukewarm running water. Never thaw or heat breast milk in a microwave, which creates hot spots and can damage the milk. Do not refreeze it once thawed.
Do these times apply to premature or hospitalized babies?
Not always. These durations are for healthy, full-term babies stored at home. For premature, ill, or hospitalized infants, storage guidance is often stricter - follow the specific instructions from your hospital or your baby's care team.
Nursing burns extra calories. If you are figuring out how much to eat while breastfeeding, try the breastfeeding calorie calculator.
These calculators give estimates based on cycle averages and standard formulas. They are for general information only and are not medical advice. For anything concerning your health or pregnancy, talk to a qualified healthcare provider.