How Long Can Prepared Formula Sit Out? Sources Compared
The short answer
The CDC says to use prepared infant formula within 2 hours of preparation and within one hour from when feeding begins (page dated May 14, 2026). Other pages differ. Health Canada counts 2 hours once feeding has started, and the AAP gives 1 hour after you finish for what is left. Table 1 shows what each counts from.
Key takeaways
- The CDC page, dated May 14, 2026, says: "use prepared infant formula within 2 hours of preparation and within one hour from when feeding begins."
- Health Canada (2025-06-27 under Page details) says for healthy, full-term infants: "Remember, once you've started feeding your child, the bottle should be used within 2 hours." The AAP table says "Up to 2 hours after preparing (1 hour if your baby has already started feeding)".
- The NHS and FDA pages give 2 hours and do not say where it starts. Neither page gives a 1 hour figure.
- For formula left in the bottle after a feed, the CDC, NHS and FDA pages say to throw it out, as does Health Canada in its section for premature, low birth weight or weakened immune system infants. None of the four gives a time. Only the AAP gives one: 1 hour once you finish feeding.
- The AAP table cell "1 hour if your baby has already started feeding" does not say where the 1 hour counts from. The AAP text on leftover formula does: once you finish feeding.
- Writing down when each feed started and ended, next to offered, left and drank, gives you the times to read against whichever page you follow.
Parents meet “1 hour” on one page and “2 hours” on another. This page opens five official pages on prepared formula and sets them side by side, with one question for each: where does the clock start? We report what each page says and pick none of them. For breast milk, see how long leftover breast milk keeps.
How long can prepared formula sit out?
Five official pages give times for prepared formula, and the clocks differ. Each row below was opened on 2026-11-01.
Table 1. What five named pages say about prepared formula, and where each clock starts
| Source | Time before feeding, or with no start named | Once feeding has started | Formula left in the bottle after the feed | Where the clock starts |
|---|---|---|---|---|
| CDC, US, May 14, 2026 | “within 2 hours of preparation” | “within one hour from when feeding begins” | “Throw out any infant formula that is left in the bottle after feeding your baby.” No time given. | 2 hours: from preparation. 1 hour: from when feeding begins |
| AAP HealthyChildren.org, US, “Last Updated 2/25/2026” | “Up to 2 hours after preparing” | “(1 hour if your baby has already started feeding)” | “Once you finish feeding your baby, any prepared infant formula left in the bottle should be thrown out within 1 hour.” | 2 hours: after preparing. 1 hour for what is left: once you finish feeding. The table cell “1 hour if your baby has already started feeding”: Not explicit |
| NHS, UK, no date shown | “Any unused formula should be thrown away if it has been kept at room temperature for over 2 hours.” Page names no start. | Not stated | “Leftover formula should be discarded at the end of a feed.” No time given. | Not stated |
| FDA, US, “Content current as of 05/17/2024” | “Use prepared infant formula within 2 hours.” Page names no start. | Not stated | “Throw away any leftover formula because it now contains the baby’s saliva, which can cause bacteria to grow.” No time given. | Not stated |
| Health Canada, powdered infant formula page, Canada, 2025-06-27 under Page details | “Serve formula as soon as possible after it has been prepared.” No time given. | Healthy, full-term infants section: “Remember, once you’ve started feeding your child, the bottle should be used within 2 hours.” Premature, low birth weight or weakened immune system section: “Once you have started feeding your child, the bottle should be used within 2 hours.” | Only in the premature, low birth weight or weakened immune system section: “All leftovers should be thrown out.” The healthy, full-term section has no sentence on it. No time given. | 2 hours: once feeding has started (both sections). A third mention, after warming prepared formula: “The bottle should be used within 2 hours.” |
“Not stated” means the page, as we read it, has no sentence on the point. It does not mean the answer is no. The wording differs too: the NHS says “over 2 hours” and the CDC says “within 2 hours”. We report the words and do not say whether they differ in effect. We could not open the WHO guideline on powdered infant formula, so it has no row.
Does the 1 hour start when the feed starts or when it ends?
The CDC counts one hour from when feeding begins, and Health Canada counts 2 hours once feeding has started. The AAP anchors its 1 hour for what is left in the bottle to the end of the feed: once you finish feeding. Its table cell “(1 hour if your baby has already started feeding)” does not say whether it counts from preparation or from the start of feeding, so table 1 marks that cell “Not explicit”.
The NHS and FDA give 2 hours and name no start. The NHS, FDA and Health Canada pages we opened have no 1 hour figure. The example below puts one bottle on each reading.
Table 2. Example, hypothetical: one bottle, four readings
Formula prepared at 10:00. The baby starts at 10:30 and stops at 10:50, a 20-minute feed.
| Reading | Counts from | Clock time |
|---|---|---|
| CDC: within 2 hours of preparation | 10:00 | 12:00 |
| CDC: within one hour from when feeding begins | 10:30 | 11:30 |
| Health Canada: 2 hours once feeding has started | 10:30 | 12:30 |
| AAP: 1 hour after you finish feeding, for what is left | 10:50 | 11:50 |
Arithmetic: 10:00 + 2 h = 12:00. 10:30 + 1 h = 11:30. 10:30 + 2 h = 12:30. 10:50 + 1 h = 11:50. The two 1 hour marks differ by the 20 minutes the feed took (11:50 minus 11:30).
The sources do not agree. Your pediatrician can tell you which reading to follow, and the label of your formula may say more.
What do the sources say about formula left in the bottle after a feed?
The FDA gives its reason in its own words: “Throw away any leftover formula because it now contains the baby’s saliva, which can cause bacteria to grow.” The CDC and NHS pages say to throw out leftover formula, and Health Canada says so in its section for premature, low birth weight or weakened immune system infants. Its healthy, full-term section has no sentence on leftovers (table 1). None of these four gives a time. The AAP is the one page that does: “any prepared infant formula left in the bottle should be thrown out within 1 hour”, counted from when you finish feeding.
What do the sources say about a bottle you will not use within 2 hours?
Four of the five pages give a fridge time for prepared formula, and the NHS gives one only for opened ready-to-feed liquid formula. Table 3 quotes them.
Table 3. What named sources say about a prepared bottle kept in the fridge
| Source | What it says about the fridge | Clock |
|---|---|---|
| CDC | “If you do not start to use the prepared infant formula within 2 hours, immediately store the bottle in the fridge and use it within 24 hours.” | 24 hours |
| AAP | Table row “Prepared infant formula”, refrigerator column: “Up to 24 hours” | 24 hours |
| FDA | “If it is not used immediately, store the bottle in the refrigerator and use it within 24 hours.” | 24 hours |
| Health Canada | “Use any prepared, refrigerated formula within 24 hours or as specified by the manufacturer.” | 24 hours, or as the manufacturer specifies |
| NHS | For a made-up feed: “If you have no choice and need to store a feed, speak to your health visitor about the best way to do this.” For opened ready-to-feed liquid formula: “for no longer than 24 hours”. | Made-up feed: Not stated. Opened ready-to-feed: 24 hours |
What do you write down when formula is left in the bottle?
Write down what you offered, what was left, what your baby drank, and the clock times the feed started and ended. The times are what let you read whichever source you follow, as table 2 shows. The log describes the feed. It does not judge it.
Example: you offer 4 fl oz (about 120 ml) of formula. When the baby stops, 1 fl oz (about 30 ml) is left. The log row reads:
| Time | Source | Offered | Left | Drank |
|---|---|---|---|---|
| 10:30 to 10:50 | Formula | 4 fl oz (about 120 ml) | 1 fl oz (about 30 ml) | 3 fl oz (about 90 ml) |
Arithmetic: 4 - 1 = 3 fl oz. In ml: 120 - 30 = 90 ml. (1 fl oz is 29.57 ml, so 4 fl oz is 118.3 ml. The ml figures here are rounded to the nearest 5 ml.)
If you want to see how much of each bottle was not drunk, the “left” column shows it over several feeds. What to do about the amount you prepare is a question for your pediatrician or your formula label.
The free bottle feeding log has columns for time, source, offered, left and drank, and a source column you set to formula. Rememilk, the bottle log we are building, is in development. The printable works without it.
What about a bottle with breast milk and formula?
The pages we opened give no time for a bottle that mixes breast milk and formula, so this page gives none. The formula times in table 1 are written for prepared formula. Our guide to what sources say about one bottle covers what the pages do say and how to log a combo bottle. The breast milk clock is on our leftover breast milk page.
What this page is, and what it is not
This page quotes five named pages and gives no medical advice. It is not a guide to preparing formula. We are parents, not medical professionals, and the sentences in table 1 belong to the sources. The page picks no winner among them and averages nothing. The AAP page says: "If your baby was born prematurely or has other health conditions, reach out to your pediatrician for additional guidance."
Pages change. Every row shows the date its page prints, or says the page shows none, and every source in the Sources list has a "Last checked" date. The how we source page explains how a source gets in. Read who writes this page for the author's role. We opened the five pages on 2026-11-01. We could not open the WHO guideline on powdered infant formula, so we use no WHO number.
Beyond the rows in the tables, this page does not cover water temperature for powdered formula, liquid concentrate, ready-to-feed shelf life or travel. Ask your pediatrician or read the label of your formula.
Frequently asked questions
How long can prepared formula sit out?
The pages we opened give different clocks. The CDC says within 2 hours of preparation and within one hour from when feeding begins, and Health Canada says 2 hours once feeding has started. The NHS and FDA say 2 hours without naming a start, and the AAP says up to 2 hours after preparing and 1 hour after you finish feeding for what is left in the bottle.
Is it a 1 hour rule or a 2 hour rule for formula?
Both numbers appear on named pages. The CDC gives 2 hours from preparation and one hour from when feeding begins, and the AAP gives 1 hour after you finish feeding for what is left. The NHS, FDA and Health Canada pages we opened give 2 hours and no 1 hour figure.
When does the 1 hour for formula start?
The CDC counts it from when feeding begins. The AAP counts its 1 hour for leftover formula from when you finish feeding, and its table cell "1 hour if your baby has already started feeding" states no starting point. The NHS, FDA and Health Canada pages give no 1 hour figure.
Can you reuse formula left in the bottle after a feed?
The CDC, NHS and FDA pages we opened say to throw out leftover formula, and Health Canada says so in its section for premature, low birth weight or weakened immune system infants. None of the four gives a time. The AAP gives 1 hour after you finish feeding.
How do you log formula wastage?
Write down what you offered, what was left and what your baby drank, plus the times the feed started and ended. Offered minus left is drank: 4 fl oz (about 120 ml) minus 1 fl oz (about 30 ml) is 3 fl oz (about 90 ml).
Does a bottle of breast milk and formula follow the formula clock?
The pages we opened do not say. None of the five gives a time for a bottle that mixes breast milk and formula, and our guide to one bottle of breast milk and formula lists what sources say.
Sources
Rememilk is a bottle milk log in development
It keeps offered, left and drank for every bottle, and nursing you cannot measure.