How long can breast milk be stored? and how?

What the evidence says

How long you can keep breast milk depends on where you store it. At room temperature (77°F/25°C or cooler), use it within about 4 hours. In the refrigerator, it's good for up to 4 days. In the freezer, aim to use it within 6 months for best quality, though up to 12 months is considered acceptable, and a separate deep freezer keeps it good a bit longer than a fridge-door freezer.

Once milk has been thawed after being frozen, it should be used within 24 hours if kept in the fridge, or within 1-2 hours if left at room temperature, and it should never be refrozen. Any milk left over after a feeding (that your baby didn't finish) should be used within 2 hours or thrown out.

A few practical tips: use clean glass or plastic containers made for breast milk storage (not disposable bottle liners or random plastic bags), label each container with the date it was expressed, and store milk toward the back of the fridge or freezer rather than in the door where temperatures fluctuate more. Always thaw the oldest milk first, and thaw it in the fridge overnight or under warm running water rather than in the microwave, since microwaving can create hot spots that burn your baby's mouth.

These guidelines are the same general framework used by Canadian and U.S. pediatric organizations, though your hospital or child care provider may have their own stricter rules, especially for premature or hospitalized babies.