Breast Milk Storage Calculator
Breast milk use-by times from pump time and storage scenario per CDC.
What it does
Breast milk keeps on strict clocks: 4 hours at room temp, 4 days refrigerated, 6 best months frozen, with thawed and leftover milk on even shorter fuses. A use-by stamp on the bottle ends the guessing.
The tool above takes pump date and time with the scenario. It returns the exact use-by stamp with the window and the rule of 4s.
The default Oct 10 08:00 fresh at room temp expires Sat Oct 10 12:00 UTC. The same pumping refrigerated runs to Wed Oct 14 08:00 UTC.
Clocks follow CDC handling pages with AAP storage guidance behind them. Both agree on 4 hours, 4 days, and the 24 hour thawed limit used here.
How to use
- Enter the pumping date.
- Enter the pumping time.
- Pick the storage scenario.
- Read the use-by stamp first.
- Read the window beside it.
- Label the bottle with both.
Formula
- start
- Pump date and time, UTC.
- window
- Scenario window in hours or days.
- rule of 4s
- 4 hours room, 4 days fridge shorthand.
Date math runs in UTC across month ends and leap days. Freezer best counts 182 days for 6 months with 12 as the outer cap. Hospitals may set stricter preterm rules that override this page.
Worked example
Example: fresh milk at room temp
Defaults: pumped Oct 10 2026 08:00, fresh at room temp.
- Pumped Oct 10 2026 at 08:00 UTC.
- Scenario: fresh at room temp, 4 hour window.
- Deadline: 08:00 + 4 hr = 12:00 UTC.
- Date line: Sat Oct 10 2026, 12:00 UTC.
- Rule of 4s printed beside it.
- Tool shows Sat Oct 10 2026, 12:00 UTC, use within 4 hours of pumping.
Reference table
| Milk | Where | Limit |
|---|---|---|
| Fresh | Room 77 F- | 4 hours |
| Fresh | Fridge 40 F | 4 days |
| Fresh | Freezer 0 F | 6 mo best, 12 max |
| Thawed | Fridge | 24 hours |
| Thawed / leftover | Room | 2 hours |
Limits
- Healthy full term guidance; hospitals differ.
- Power outages need separate food rules.
- Estimates for information only.
- Smell and taste never override clocks.
Common mistakes
- Stretching 4 hours to 5.
- Refreezing thawed milk.
- Microwaving bottles.
- Storing in fridge doors.
- Thawing oldest last.
Try it yourself
Quick checks. Answers sit tucked under each question.
Fresh refrigerated from Oct 10 08:00?
Oct 10 08:00 + 4 days = Wed Oct 14 2026, 08:00 UTC.
Leftover started 14:00 Oct 10?
14:00 + 2 hr = Sat Oct 10 2026, 16:00 UTC, then discard.
Thawed milk timing?
Thawed fridge counts 24 hr from full thaw; room counts 2 hr from warming.
Questions
How long does fresh milk last out?
Up to 4 hours at 77 F or colder, then refrigerate or use.
How long in the fridge?
Up to 4 days in the back at 40 F. Freeze by day 4 if unused.
How long frozen?
6 months best, 12 acceptable at 0 F or colder. Deep freeze holds longest.
How long after thawing?
Best within 24 hours after fully thawed; use within 2 hours once warmed. Never refreeze.
What about bottle leftovers?
Use within 2 hours of the feed, then discard. Store 2 to 4 oz portions to cut waste.
Can I microwave milk?
No. Microwaves heat unevenly and scald; warm in water and swirl to mix.