Breast milk in a bottle.
Pumped milk, from the fridge to the bottle. Plenty of families feed both breast milk and formula. This page is for the breast milk part.
Every answer here is checked by an International Board Certified Lactation Consultant, the clinical credential for infant feeding. Where our IBCLC’s guidance differs from a published source, the answer says so.
Step 1: How long it keeps
4–6 hours out. 4–6 days in. Months frozen.
- Counter
- 4–6 hours
- Fridge
- 4–6 days
- Freezer
- 6 monthsbest · up to 12 is OK
| Cooler with ice packs | Up to 24 hours |
|---|---|
| Warmed, or at room temperature | Use within 2 hours |
| Thawed from frozen | Keep chilled. Use within 24 hours. |
| Left in the bottle after a feed | Use within 2 hours, then throw it out |
Sources: CDC; Mayo Clinic Counter and fridge times: guidance from our IBCLC
Step 2: Storing
Small portions. Dated. Back of the fridge.
- What in Breast milk storage bags, or a clean food-grade glass or plastic container with a tight lid. Not bottle liners or ordinary plastic bags.
- How much 2–4 oz, or one feed’s worth. Leave about an inch at the top: milk expands when it freezes.
- Label it The date you pumped, in waterproof pen. Going to daycare? Add your baby’s name.
Use the oldest milk first. Store it at the back of the fridge or freezer, not in the door, where the temperature changes every time it opens. Small portions mean less goes down the sink.
Chill it first, then combine. Go by the oldest date.
That’s the CDC’s advice, so the cold milk doesn’t rewarm. No published study shows that adding fresh milk straight in causes harm, and many families do. Either way, the combined milk takes the date of the oldest milk in it.
Sources: CDC; Mayo Clinic; MedlinePlus; Nemours KidsHealth; NHS
Step 3: Thawing
Overnight in the fridge is easiest.
- Oldest firstMove it to the fridge the night before.
- Need it sooner?Hold the sealed container under warm running water, or stand it in a bowl of warm water.
- Use within 24 hoursDon’t refreeze it. Still has ice crystals? It can go back in the freezer.
Never the microwave or the stove. Parts get very hot while others stay frozen.
Sources: Mayo Clinic; CDC
Step 4: Mixing with formula
Breast milk and formula, same bottle? Yes.
Make the formula first, exactly as the label says. Then add the breast milk.
The short version.
Breast milk in a bottle in 4 lines.
How long it keeps 4–6 hours on the counter, 4–6 days in the fridge, 6 months in the freezer.
Storing Small portions, dated, at the back of the fridge. Use the oldest first.
Thawing Thaw overnight in the fridge and use it within 24 hours. Never the microwave.
Mixing with formula Breast milk and formula in one bottle is fine: make the formula first, then add the breast milk.