Breast Milk and Formula in One Bottle: What Sources Say

The times for leftover breast milk are on our leftover breast milk guide. This page covers what sources say about one bottle, and how to write a combo bottle down.

What do official sources say about mixing breast milk and formula in one bottle?

The health agency pages we opened say nothing about one bottle. Table 1 also lists a charity, a lactation site and three formula makers, each labelled by type. All rows were opened on 2026-10-25.

Table 1. What named sources say about mixing breast milk and formula

“Not stated” means the page, as we read it, has no sentence on the point. It does not mean the answer is no. The table picks no winner and averages nothing. The formula-maker rows are web pages from the makers, not a product label, and we did not open a label. For your formula, read the label.

We searched for AAP, WHO and Mayo Clinic pages on putting both in one bottle and did not open one. Their absence from table 1 says nothing about what those bodies think. How we source explains how a page gets into a table.

Why do parents get different answers?

Because the pages differ. In table 1, the health agency and health service pages are silent on one bottle, La Leche League Canada and KellyMom say to keep them separate, and the formula makers describe how to combine them or send you to your pediatrician.

Individual clinicians quoted in parenting magazines add more views. In a Romper article (by Jessica Booth, updated Feb. 20, 2024), pediatrician Maya Muñoz Mahmood, described there as a Fellow of the American Academy of Pediatrics, says: “As a broad rule, I don’t recommend mixing them in the same bottle.” That is one clinician’s personal view as quoted by a magazine. It is not AAP policy, and the AAP page in table 1 does not mention mixing.

The CDC’s “breast milk first, then formula” line is on its emergency feeding page, not on the two storage pages. It is about the order of feeds. The page does not mention one bottle.

What changes about leftover milk when a bottle is mixed?

No health agency, health service or charity page in table 1 gives a time for a mixed bottle, so this page gives none in its own voice. The one time in table 1 is a formula maker’s. The times for leftover breast milk, quoted from named sources, are on the leftover guide for breast milk. Fresh and thawed breast milk times from named sources are in the storage times from named sources table.

The CDC’s 2 hours is written for leftover breast milk. The CDC formula page gives separate times for prepared formula: “within 2 hours of preparation and within one hour from when feeding begins”. Bobbie, a formula maker, gives its own wording for a mixed bottle in table 1. The CDC pages do not give a time for a mixed bottle.

How do you write down a combo bottle?

Write one bottle at one sitting as one feed, with the parts and a total. Table 2 shows three ways.

Table 2. Three ways to write down a combo bottle

In words, one line reads: breast milk 2 fl oz (about 60 ml) + formula 1 fl oz (about 30 ml) = 3 fl oz (about 90 ml) offered.

Example: pumped milk 2 fl oz (about 60 ml) + formula 1 fl oz (about 30 ml) = 3 fl oz (about 90 ml) offered. When the baby stops, 0.5 fl oz (about 15 ml) is left. Drank: 3 - 0.5 = 2.5 fl oz, or 90 - 15 = 75 ml. (1 fl oz is 29.5735 ml, so 3 fl oz is 88.7 ml. The ml figures here are rounded to the nearest 5 ml.)

If you want a number for each source, one method is to split what the baby drank in proportion to what went into the bottle. Pumped milk was 2 of 3 parts and formula was 1 of 3 parts:

• Pumped milk: 2/3 x 75 ml = 50 ml (about 1.7 fl oz).
• Formula: 1/3 x 75 ml = 25 ml (about 0.85 fl oz).

This is an estimate. It assumes the bottle was mixed evenly and that the baby took the same share of each part.

Logging one bottle as one feed counts that sitting once. Two separate entries for one bottle would count one feed twice: six combo bottles in a day read as 6 feeds, not 12. The printable bottle feeding log has a mixed-bottle line for this. Rememilk, the bottle log we are building, is in development. The printable works without it.

What if you cannot measure breastfeeding?

A nursing session has no ml you can read, so write it as “not measured” with the minutes per side, never as 0 ml. A day total then reads “X ml measured + N nursing sessions not measured”. Example: “450 ml (about 15 fl oz) measured + 3 nursing sessions not measured”. The printable has a nursing row for this.