Every breast milk bag needs at least two things written on it: the date the milk was expressed and your baby’s name (especially if the milk is going to daycare). Beyond those basics, a few extra details on the label and a consistent system will keep your milk organized, safe, and easy to rotate through before it expires.
What to Write on Every Bag
At minimum, write the date you pumped the milk. This is the single most important piece of information because storage time limits start from the moment milk is expressed, not from when it goes into the fridge or freezer. If you’ve combined milk from more than one pumping session across different days, use the earlier date.
Beyond the date, here’s what’s worth adding:
- Time of day. Helpful if you’re pumping multiple times a day and refrigerating bags before combining or freezing them. It also lets you grab the oldest bag first when several share the same date.
- Volume in ounces. Knowing how much is in each bag saves you from thawing more than your baby needs. Most breast milk bags have measurement markings printed on them, so just note the volume before you seal and lay the bag flat. Keep in mind that milk expands slightly when frozen, so the markings may look off once the bag is solid.
- Your baby’s name. Required for daycare or any setting where multiple children’s milk is stored together. Write both first and last name to prevent mix-ups.
- Any dietary notes. If you consumed something your baby reacts to, or if you took medication that day, a quick note can help you or a caregiver make informed choices later.
Best Markers and Labels for Freezer Storage
The biggest frustration with labeling breast milk bags is ink that smears or disappears in the freezer. Condensation forms on cold bags, and many pens simply wipe right off the plastic surface. A permanent marker like a Sharpie is the most reliable option. Despite being “permanent,” Sharpies are classified as non-toxic by the manufacturer, and since you’re writing on the outside of a sealed bag, the ink never contacts the milk.
If you prefer something neater, a handheld label maker (like the Brother P-Touch) prints adhesive labels that stick well to bags even at freezer temperatures. This is especially useful if your handwriting gets hard to read on small plastic surfaces. Some parents also use pre-printed freezer labels designed specifically for breast milk bags, which have blank fields for date, time, and volume. These peel-and-stick labels work well as long as you press them firmly onto a dry bag surface.
When to Label: Before You Fill
Write on the bag or apply your label before you pour milk in. A flat, dry, empty bag is far easier to write on than a full, slippery one. Most breast milk storage bags have a designated white or frosted writing area near the top, and ink adheres best to a clean, dry surface. Once milk is inside, the bag curves and flexes, making neat writing difficult and increasing the chance you’ll accidentally puncture the bag with a pen tip.
If you’re not sure how much milk will go into the bag (because you’re still pumping), leave the volume blank and fill it in right after sealing. Everything else, including date, time, and name, can go on before you start.
Organizing Bags for First-In, First-Out Rotation
Labeling only helps if you actually use the oldest milk first. Freshly expressed milk stays good for up to 4 hours at room temperature, up to 4 days in the refrigerator, and about 6 months in the freezer (up to 12 months is acceptable, but quality declines after 6). Those timelines make a first-in, first-out system essential, especially for a growing freezer stash.
A simple approach: lay bags flat to freeze them, then stand them upright in a bin or container sorted by date, with the oldest bags in the front. Some parents group bags into gallon-sized zip-top bags by week or date range, then write the date range on the outer bag with a marker. That way you can grab the oldest group without digging through individual bags. When you need milk, always pull from the front of the oldest group first.
If your freezer stash grows beyond a single bin, consider numbering your zip-top groups so you know at a glance which one to reach for next. A small dry-erase board on the freezer door with your current date ranges can save time, too.
Labeling for Daycare and Childcare
Childcare centers have stricter labeling requirements because they’re handling milk for multiple babies. The CDC recommends that every bottle or bag delivered to childcare include the child’s full name and the date. For frozen milk dropped off at daycare, the label should show the date the milk was originally expressed, not the date you’re delivering it.
Many daycare centers also suggest color-coded labels, personalized stickers, or silicone bands to help caregivers quickly identify which milk belongs to which child. Ask your daycare about their specific policy before your baby’s first day. Some centers want labels on the cap of every bottle in addition to the body, and some require first and last name written in a specific location. Getting this right from the start prevents the stressful phone call about unlabeled milk that can’t be used.
If you send multiple bags for a single day, number them in the order you’d like them used (Bag 1 of 3, Bag 2 of 3, etc.). This helps caregivers serve the oldest milk first without needing to compare pump dates and times.
Labeling Thawed Milk
Once you thaw a frozen bag, the clock resets on storage time. Thawed breast milk is safe in the refrigerator for up to 24 hours from the time it fully thaws, and it should never be refrozen. Add a quick “thawed” note with the date and time you moved it to the fridge. This is easy to forget in the haze of early parenthood, but it matters: thawed milk that sits too long looks and smells normal, so you can’t tell by inspection alone whether it’s still within the safe window.
A small piece of masking tape works well for adding thaw information to a bag that’s already been labeled, since writing over existing ink on a wet or cold surface rarely turns out legible.