--- title: "How long to try a formula before switching" description: "Nobody publishes a trial length, and the NHS says there is no evidence switching helps or harms. What to watch, and when to ask a health visitor." url: https://milkatlas.com/guides/choosing/how-long-to-trial-a-formula/ language: en dateModified: 2026-09-23 --- Guide · Choosing a HiPP formula # How long to trial a formula Written by [Kseniia P.](https://milkatlas.com/about/kseniia/) and [Tatum G.](https://milkatlas.com/about/tatum/) Written with AI assistance. Published 23 September 2026 Medically reviewed [Dr. Jill Palko](https://milkatlas.com/medical-review/) · MD, FACOG · [Registration NPI 1093033011](https://npiregistry.cms.hhs.gov/provider-view/1093033011) · 8 October 2026 Next review due 8 October 2027 ## The answer No manufacturer publishes a trial length for a formula, and no trial we could find measures one. What the NHS does say is that there is no evidence switching to a different formula does any good or harm, and that if you think a brand disagrees with your baby you should talk to a midwife or health visitor. So the honest answer is not a number of days. It is a short list of things to watch, of which weight gain is the only one that settles anything. ## Key takeaways - There is no published trial length for any HiPP formula, and the packs give none. - The NHS says there is no evidence that switching formula does any good or harm. - The two to four weeks that circulates is ESPGHAN's diagnostic elimination diet, run under a doctor with a test at the end. - Stools, wind and a changed feeding pattern are common on any change and settle nothing on their own. - Weight gain is the measure that turns a set of ordinary symptoms into a reason to see someone. ## In this series - [Choosing a HiPP formula · hub]() - [Switching HiPP stages · guide]() - [Who HiPP is not for · guide]() ## Is there a published answer? No. No HiPP pack gives a trial length or a timescale, and we could find no trial that measures one for any formula. (Source 4) Evidence · No evidence found This is an absence rather than a finding. Nobody has run the study, so anyone quoting you a number of days has reasoned their way to it, as we do below, rather than read it somewhere. What is published is the question behind it, and the NHS answers that directly: there is no evidence that switching to a different formula does any good or harm, and if you think a particular brand disagrees with your baby, talk to a midwife or health visitor, who can help you decide whether to try a different type. (Source 1) That reframes the page. The question is not how long to wait before switching. It is whether switching is the thing to do at all. ## Where does the two to four weeks come from? A different question, and one worth separating carefully, because the figure circulates as though it were a trial length. ESPGHAN recommends a short diagnostic elimination diet of two to four weeks, followed by a challenge test, as the cornerstone of diagnosing a cow's milk allergy. (Source 2) That is a supervised procedure with a test at the end, prescribed for a baby under investigation. It is not two to four weeks of trying a tin to see how it goes, and it is not advice about choosing between ordinary formulas. Borrowing the number for that is the commonest misreading on this subject. ## What is actually worth watching? Weight, and whether feeds are being taken. Those two answer the question. Most of what parents watch instead does not. ESPGHAN is direct about the rest. Changes in stool characteristics, feeding aversion, or occasional spots of blood in stool are common and in general should not be considered diagnostic of a cow's milk allergy, and green or mucous stools should not be considered as symptoms of it in otherwise presumed healthy infants. (Source 2) It says that as a caution against over-diagnosis, which it reports is more common than under-diagnosis, and it names what a wrong diagnosis costs: acute reactions, growth faltering, micronutrient deficiencies, and a worse quality of life for the baby and the people caring for them. (Source 2) Evidence · No evidence found A paediatric society's position rather than a trial, and a statement about what symptoms do not establish rather than about how long to wait. It is still the most useful published thing on the question. ## If you do change, how? One feed at a time. HiPP's advice for moving between its own milks is to replace one bottle a day, adding a bottle of the new formula each day, and never to mix two powders in the same bottle. (Source 3) Two practical notes. The scoops are not interchangeable between packs, so measure each powder with the scoop that came with it. And because every feed is made fresh, a changeover is counted in feeds rather than in days of milk already made up. (Source 5) ## When is the answer a person rather than another tin? When a baby is not gaining weight. When symptoms are getting worse rather than settling. When a reaction frightens you. At any of those points the useful next step is a diagnosis, not a different brand, and the NHS puts the same decision in the hands of a midwife or health visitor rather than the shelf. (Source 1) (Source 2) Our view Give a change of formula a fortnight, and judge it on feeding and weight rather than on nappies. That is our reasoning and not a finding: a fortnight is long enough to see past the first unsettled days and short enough that you are not waiting on a baby who is losing ground. If the baby is growing and feeding, a different-looking stool is not a reason to change again. If the baby is not, no tin on any shelf is the answer and the appointment is. ## Products mentioned - [HiPP German PRE](https://milkatlas.com/formula/combiotik/hipp-german-pre/) 2060-02 · 600 g box · Sold - [HiPP German Stage 1](https://milkatlas.com/formula/combiotik/hipp-german-stage-1/) 2031-02 · 600 g box · Sold - [HiPP German HA 1](https://milkatlas.com/formula/hypoallergenic/hipp-german-ha-1/) 2142-03 · 600 g box · Sold - [HiPP German Comfort](https://milkatlas.com/formula/special/hipp-german-comfort/) 2313 · 600 g box · Sold ## Questions parents ask ### How long should I give a new formula? Nobody publishes a figure, so anyone who gives you one is guessing. A fortnight is a reasonable practical answer if a baby is feeding and gaining, because it is long enough to see past the first few days of any change, but it is our reasoning rather than a finding. ### Is switching formula safe? The NHS says there is no evidence that switching to a different formula does any good or harm, and that a midwife or health visitor can help you decide whether to try a different type. ### Where does the two to four weeks come from? A different question. ESPGHAN recommends a short diagnostic elimination diet of two to four weeks, followed by a challenge test, as the cornerstone of diagnosing a cow's milk allergy. That is a supervised procedure with a test at the end, not a period of trying a tin from the shelf, and quoting it as a trial length for an ordinary formula misreads it. ### What should change if a formula suits? Less than people expect, which is the part that catches people out. A baby who was feeding and gaining before will carry on doing both. ### What about stools? They change on any change of formula, and they settle nothing on their own. ESPGHAN's position paper says changes in stool characteristics, feeding aversion and occasional spots of blood are common in infants and should not in general be considered diagnostic of a cow's milk allergy, and that green or mucous stools are not symptoms of it in an otherwise presumed healthy infant. That is a caution against over-diagnosis. ### What is actually worth watching? Weight, and whether feeds are being taken. Those two answer the question between them; the nappies, which are what most parents watch, mostly do not. ### How do I change over? HiPP's own advice for moving between its milks is to replace one feed a day, adding a bottle of the new formula each day, and never to mix two powders in the same bottle. The switching guide has the schedule, and the scoops are not interchangeable between packs. ### Can I go back if it does not suit? Yes, on an ordinary formula, and the same bottle-by-bottle method applies. If a health professional chose the formula, ask them first. ### When should I stop trying tins? When a baby is not gaining weight, when symptoms are getting worse rather than settling, or when a reaction frightens you. ESPGHAN warns that over-diagnosis of cow's milk allergy is more common than under-diagnosis and that a wrong diagnosis carries growth faltering and micronutrient deficiencies of its own, so the useful next step at that point is a diagnosis rather than another brand. ### Does the stage number matter while I am working this out? No. A first infant formula can be a baby's main drink for the whole first year, so there is no clock running alongside the one you are watching. ## Sources How this page was checked - Sources verified · 23 Sept 2026 - External links · opened and read 23 Sept 2026 - Product data · snapshot 2026-10-15 - Editorial review · 23 Sept 2026 - Next scheduled check · 23 Oct 2026 1. [NHS, Types of formula](https://www.nhs.uk/baby/breastfeeding-and-bottle-feeding/bottle-feeding/types-of-formula/) · there's no evidence that switching to a different formula does any good or harm; if you think a particular brand disagrees with your baby, talk to a midwife or health visitor; first infant formula is the only formula a baby needs in the first year · fetched 23 September 2026 2. [Vandenplas Y. et al., 2024, Journal of Pediatric Gastroenterology and Nutrition 78(2):386-413](https://pubmed.ncbi.nlm.nih.gov/38374567/) · ESPGHAN position paper on cow's milk allergy: the two to four week diagnostic elimination diet followed by a challenge test; changes in stool, feeding aversion and occasional spots of blood are common and not diagnostic; green or mucous stools are not symptoms in an otherwise presumed healthy infant; over-diagnosis is more common than under-diagnosis, and a wrong diagnosis carries growth faltering and micronutrient deficiencies · fetched 23 September 2026 3. [HiPP Germany, Was muss ich beim Umstellen von Milchnahrungen beachten?](https://www.hipp.de/ratgeber/saeuglingsalter/milchnahrung-flaeschchen/was-muss-ich-beim-umstellen-von-milchnahrungen-beachten) HiPP's advice on changing between its milks: replace one feed a day, adding a bottle of the new formula each day, and never mix two powders in the same bottle · fetched 23 September 2026 4. [HiPP pack artwork for HiPP 1 Bio Combiotik 600 g, version 8 (May 2025)](https://cdn.sanity.io/files/2xwg8lcu/production/3bee0b8de419e761eeaf591a208104b142236ce6.pdf) · the pack: a feeding chart by age, a scoop weight, and no trial length or timescale anywhere on it · fetched 23 September 2026 5. [NHS, Making up baby formula](https://www.nhs.uk/baby/breastfeeding-and-bottle-feeding/bottle-feeding/making-up-baby-formula/) · feeds are made fresh for each feed, which is why a changeover is counted in feeds rather than in days of prepared milk · fetched 23 September 2026 **Corrections (0)** None since this page was published. [How we correct mistakes](https://milkatlas.com/corrections/)