For healthy, full-term babies, US CDC guidance allows freshly expressed milk for up to 4 hours at 77°F (25°C) or cooler, 4 days in the refrigerator, and about 6 months in the freezer for best quality; up to 12 months is acceptable. UK NHS guidance allows up to 8 days at the back of a refrigerator kept at 4°C or colder and up to 6 months at −18°C or colder. Follow the guidance for the country where you receive care. If your baby was born prematurely, is in hospital, or has additional health needs, use the plan from your care team.
Before you store milk
Wash your hands and clean pump parts according to the manufacturer's instructions. Use breast milk storage bags or clean, food-grade containers with tight lids. Label each portion with the date and time, leave room for expansion when freezing, and store it at the back rather than in the door.
Why the 3-3-3 rule is not enough
Three hours out, three days refrigerated, and three months frozen is easy to remember, but it does not show the temperature or whether the milk is fresh, thawed, or already offered to the baby. Use the official times above as upper limits, freeze milk early if you will not use it in time, and use the oldest portion first.
Thaw and warm it safely
Thaw milk overnight in the refrigerator, in lukewarm water, or under lukewarm running water. Do not use a microwave or heat it directly on the stove. Under CDC guidance, use milk within 24 hours of being fully thawed in the refrigerator, or within 2 hours once it has warmed or reached room temperature. Never refreeze fully thawed milk.
What about an unfinished bottle?
CDC guidance says to use milk left after a feed within 2 hours, then discard it. NHS guidance advises discarding any milk left after feeding. Starting with a small amount and adding more if needed can reduce waste.
Can milk from different pumping sessions be combined?
Cool newly expressed milk before adding it to milk that is already chilled.
Date the combined container from the oldest milk inside it.
Related baby guide
For feeding, diaper output, weight checks, and signs that need medical attention in the first days, continue with the newborn guide.
View references and primary sources
- US Centers for Disease Control and Prevention — Breast Milk Storage and Preparation25 March 2026 · accessed September 2026
- US Centers for Disease Control and Prevention — Storage Questions and Answersaccessed September 2026
- NHS — Storing breast milkaccessed September 2026