Formula feeding: the complete guide

Formula feeding is how millions of parents nourish their babies every day. Whether you are exclusively formula feeding from birth, supplementing breastfeeding, or transitioning from breast to bottle, this guide covers everything you need: choosing the right formula, preparing it safely, how much to give at each age, and how to recognise signs that something is not agreeing with your baby.

One thing first: formula is a safe, regulated, nutritionally complete way to feed a baby. It contains all the nutrients an infant needs in the first 12 months. The choice to formula-feed — whatever the reason — is a valid one.

Choosing a formula

Standard cow's milk-based formula

For the vast majority of healthy babies, standard first infant formula based on modified cow's milk protein is the right starting point. All infant formulas sold in the UK, EU, and US are regulated and must meet the same nutritional standards.¹ Brand differences are largely marketing rather than meaningful nutritional variation.

"Stage 1" (first infant formula) is appropriate from birth throughout the first year. There is no nutritional justification for switching to "Stage 2" (follow-on formula) — follow-on formulas are not recommended for babies under 6 months and are not nutritionally necessary at any stage.²

Partially hydrolysed formula

Partially hydrolysed formulas have cow's milk proteins broken down into smaller fragments. They are marketed for "comfort" or as suitable for fussy, gassy babies. The evidence for meaningful benefit over standard formula in healthy babies is weak.³ They are not a treatment for cow's milk protein allergy (CMPA).

Extensively hydrolysed formula

Extensively hydrolysed formula (eHF) has proteins broken down to a level that most babies with CMPA can tolerate. It is used as a first-line treatment for confirmed or suspected CMPA and should be used on medical advice, not self-prescribed.⁴

Amino acid formula (elemental formula)

Used for babies who cannot tolerate eHF — around 10% of CMPA cases. Strictly prescribed.

Lactose-free formula

Contains cow's milk protein but with lactose replaced by another carbohydrate. Appropriate for temporary lactase deficiency after gastroenteritis, not for CMPA (the problem in CMPA is the protein, not the lactose).⁵

Soy-based formula

Not recommended as a routine first choice, due to phytoestrogen content and because up to 50% of babies with CMPA also react to soy protein.⁴ Used occasionally for specific dietary or cultural reasons under medical guidance.

Preparing formula safely

Safe preparation is not optional advice — it is a genuine safety issue. Powdered infant formula is not sterile. It can contain Cronobacter sakazakii (formerly Enterobacter sakazakii) and Salmonella, which can cause severe, life-threatening infection in young infants. High-temperature water kills these bacteria; water below 70°C does not.⁶

Step-by-step preparation (NHS guidance)⁶

1. Boil fresh tap water (not previously boiled) and leave to cool for no more than 30 minutes — this gives water at approximately 70°C.
2. Clean and sterilise all bottles, teats, and equipment before use.
3. Pour the correct amount of hot water into the sterilised bottle first.
4. Add the exact number of level scoops of powder — do not pack, heap, or round the scoops. Use the scoop from the formula tin, levelled off with a clean knife or the built-in leveller.
5. Seal the bottle and shake well to dissolve.
6. Cool quickly under cool running water or in a bowl of cold water until the formula is comfortable on the inside of your wrist (body temperature, not warm).
7. Feed immediately. Discard any formula left in the bottle after a feed — do not save it.

Prepared formula can be stored in the back of the fridge (4°C or below) for up to 24 hours if not used immediately. Never warm formula in a microwave — hot spots can form and scald.

Ready-to-feed formula

Ready-to-feed (liquid) formula is sterile, requires no mixing, and carries no Cronobacter risk from preparation. It is more expensive than powder but useful when precise safe preparation is difficult (travel, night feeds, hospital). Once opened, use within 2 hours at room temperature or within 24 hours if refrigerated.

How much formula by age

These are guide amounts. Every baby is different — some need slightly more, some slightly less. The cues that your baby has had enough (turning away, slowing sucking, relaxing hands) matter more than hitting a specific volume.⁷

After 6 months, solid foods begin to complement milk feeds — milk remains the primary nutrition source until 12 months. Total formula volume gradually decreases as solid intake increases.

Babies should not be given more than 1 litre (1,000 ml) of formula per day on a routine basis.² More than this can reduce appetite for solids when they start, and iron in formula becomes less bioavailable at very high volumes.

Paced bottle feeding

Standard bottle feeding allows formula to flow freely and quickly — a baby can take a large volume in a short time and may not register fullness before they've overfed. Paced bottle feeding mimics the effort and pace of breastfeeding and allows babies to self-regulate intake.

How to pace a bottle feed:

• Hold the baby in a more upright position (not lying flat)
• Hold the bottle horizontally, so the teat is about half full — not angled fully up
• Let the baby draw the teat in themselves rather than pushing it in
• After every 20–30 sucks, tilt the bottle down briefly so the teat empties — this gives a natural pause, as happens at the breast
• Watch for full cues: turning away, slowing down, releasing the teat, relaxing hands⁸

Paced feeding helps reduce overfeeding, can reduce gas, and is particularly useful when combination feeding to avoid bottle preference.

Storing prepared formula

• Made-up formula (powder + hot water): use immediately, or refrigerate for up to 24 hours. Do not freeze.
• Opened ready-to-feed formula: use within 2 hours if kept at room temperature, within 24 hours if refrigerated.
• Opened powder tin: use within 4 weeks of opening (most tins specify this on the label). Store in a cool, dry place — not the fridge.

Never keep formula that has been partly consumed — bacteria from the baby's mouth transfer into the bottle and multiply rapidly.⁶

Recognising cow's milk protein allergy vs lactose intolerance

These two conditions are often confused but are different in cause and management.

Cow's milk protein allergy (CMPA) is an immune response to the proteins in cow's milk. Symptoms include: persistent eczema or skin rash, blood or mucus in stool, vomiting, chronic diarrhoea, poor weight gain, significant reflux, or colic that does not resolve. CMPA affects approximately 2–3% of formula-fed babies.⁴ Treatment involves switching to an extensively hydrolysed formula (or amino acid formula in severe cases) under GP guidance.

Lactose intolerance is a deficiency of the enzyme lactase, making it difficult to digest lactose (the sugar in milk). True congenital lactose intolerance is extremely rare in infants. Temporary lactase deficiency can occur after gut infection — in this case, lactose-free formula may be used short-term until the gut recovers.⁵ Lactose intolerance does not cause immune reactions, eczema, or blood in stool.

If you suspect CMPA: speak to your GP. They can advise on a trial of hypoallergenic formula and refer to a paediatric dietitian if needed. Do not self-prescribe hypoallergenic formula without a diagnosis, as it makes diagnosis harder and the formulas are expensive.

Switching formulas

Switching between standard cow's milk-based formulas (same stage, different brand) is safe and does not require a transition period. Stool consistency and frequency may change slightly, which is normal.

Switching to a different type of formula — for example, moving to a hydrolysed formula for suspected CMPA — should be done on medical advice where possible.

If your baby seems to be struggling with a formula (excessive gas, persistent crying, unusual stools), speak to your health visitor or GP before switching repeatedly. Many of these symptoms have other causes, and formula-switching without guidance can lead to unnecessary expense and delayed diagnosis.

Combination feeding

Many families combine breast and bottle — breast milk for some feeds, formula for others. The practical points:

• Effect on supply: giving formula in place of a breast feed will reduce supply at that time if the breast is not pumped instead. If you want to maintain supply, pump whenever you substitute a formula feed.
• Timing: combination feeding is easier to establish after breastfeeding is going well (typically 4–6 weeks), though it can be started earlier for medical reasons.
• Bottle preference: some breastfed babies resist the bottle; others prefer it once they've had it. Paced bottle feeding helps reduce the risk of bottle preference overtaking breast.

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Sources

1. NHS. "Types of infant formula." NHS, 2024. https://www.nhs.uk/conditions/baby/breastfeeding-and-bottle-feeding/bottle-feeding/types-of-infant-formula/
2. Scientific Advisory Committee on Nutrition. "Feeding in the First Year of Life." Public Health England, 2018. https://www.gov.uk/government/publications/feeding-in-the-first-year-of-life-sacn-report
3. Szajewska H, Horvath A. "A partially hydrolyzed 100% whey formula and the risk of eczema and any allergy." J Allergy Clin Immunol 130(2), 2012. https://pubmed.ncbi.nlm.nih.gov/22743302/
4. NHS. "Cows' milk protein allergy in babies." NHS, 2024. https://www.nhs.uk/conditions/baby/breastfeeding-and-bottle-feeding/bottle-feeding/cows-milk-protein-allergy/
5. NHS. "Lactose intolerance." NHS, 2024. https://www.nhs.uk/conditions/lactose-intolerance/
6. NHS. "Making up infant formula." NHS, 2024. https://www.nhs.uk/conditions/baby/breastfeeding-and-bottle-feeding/bottle-feeding/making-up-infant-formula/
7. American Academy of Pediatrics. "Amount and Schedule of Formula Feedings." HealthyChildren.org, 2023. https://www.healthychildren.org/English/ages-stages/baby/feeding-nutrition/Pages/Amount-and-Schedule-of-Formula-Feedings.aspx
8. NHS. "Bottle feeding advice." NHS, 2024. https://www.nhs.uk/conditions/baby/breastfeeding-and-bottle-feeding/bottle-feeding/bottle-feeding-advice/