Combination Feeding: How to Mix Breastfeeding and Formula

Combination feeding, also called mixed feeding, simply means your baby gets both breast milk and formula. Some parents plan it from the start. Others add formula because of low supply, a return to work, a medical reason, or simply because they need more rest and help with feeds. All of these are valid reasons.

Combination feeding can work well for years, or it can be a bridge back to more breastfeeding. Either way, a little planning helps you keep the breast milk you want while giving formula safely. Here’s how to start, how to protect your supply, and how to prepare formula the way the CDC recommends.

What combination feeding looks like

There’s no single right pattern. Common setups include:

• Breastfeeding most of the time, with one or two formula bottles a day, for example an evening feed someone else can give.
• Breastfeeding when you’re together and formula while you’re apart, such as at daycare or during work shifts.
• Topping up after breastfeeds with a small amount of formula when your baby’s doctor has advised extra milk.
• Pumped breast milk plus formula in bottles, if your baby doesn’t feed at the breast.

You can also give expressed breast milk and formula in the same bottle, as long as the formula is made up with water first. Our guide to mixing breast milk and formula explains the safe order and timing.

How to start combination feeding

Go slowly

The NHS recommends cutting back breastfeeds gradually rather than all at once. Start by replacing one breastfeed a day with a bottle. Your breasts may take about 5 to 7 days to adjust each time you drop a feed, so give each change time before making the next one. Going slowly also lowers your risk of overfull breasts, leaking and mastitis.

Pick the first feed to swap

Choose a feed that is easiest for your routine, often one where a partner or caregiver can help. Many parents choose the bedtime feed, hoping it helps their baby sleep longer. The NHS notes that this is unlikely to help a newborn, who needs to feed little and often anyway.

Offer breast milk first when you can

When you’re supplementing, the AAP suggests starting feeds with the breast milk you have, then giving formula if your baby still needs more. That way none of your milk goes to waste.

Use responsive bottle feeding

Let your baby set the pace and the amount. Hold your baby fairly upright, let them pause, and stop when they show they’re full rather than encouraging them to finish the bottle. Paced bottle feeding is a simple way to do this, and it can make switching between breast and bottle easier.

Protecting your milk supply

Your body makes milk in response to how often and how well milk is removed. Each breastfeed you replace with formula sends a signal to make a little less. The NHS is clear that introducing formula will probably reduce your breast milk supply. That’s not a reason to avoid it, but it helps to plan:

• Keep breastfeeding regularly at the feeds you want to keep. Feeding on demand at those times helps.
• Pump when you miss a feed if you want to keep your current supply, for example while you’re at work. Our pumping schedule guide has sample routines for work days and nights.
• Make changes one at a time so you can see how your body responds.
• Watch for engorgement. If your breasts feel hard, hot or painful after dropping a feed, express a little milk for comfort and cut back more slowly.

If your supply has dropped and you want more breast milk again, frequent, effective milk removal is the main tool. See how to increase milk supply for practical steps. Specific “milk-boosting” foods or supplements aren’t necessary, according to the AAP.

How to prepare formula safely (CDC steps)

Powdered formula is the type most families use to supplement. It is not sterile, so careful preparation matters. The CDC recommends:

1. Wash your hands with soap and water, and clean your work surface and bottles.
2. Use water from a safe source. If you’re not sure your tap water is safe, contact your local health department.
3. Measure the water first, then add the powder, using exactly the amount on the container. Too much water can leave your baby short on nutrients, and too little can cause dehydration.
4. Shake to mix. Formula doesn’t need to be warmed. If you do warm it, put the bottle under warm running water. Never use the microwave.
5. Test a few drops on your wrist. It should feel warm, not hot.

The AAP adds that formula diluted with too much water can cause serious health problems, including seizures from water intoxication, so never stretch formula with extra water.

Extra care for young or vulnerable babies

If your baby is younger than 2 months, was born before 37 weeks, or has a weakened immune system, the CDC recommends extra precautions with powdered formula. Boil the water, wait about 5 minutes, then mix the formula while the water is still hot. Water around 158°F (70°C) is hot enough to kill germs such as Cronobacter. Let the bottle cool and test it on your wrist before feeding. Ask your baby’s doctor whether liquid ready-to-feed formula, which is sterile, would be a better choice.

How long prepared formula lasts

Situation	CDC guidance
At room temperature after mixing	Use within 2 hours
Once your baby starts drinking	Use within 1 hour, then throw away leftovers
Not used within 2 hours	Refrigerate right away and use within 24 hours
Opened container of powder	Keep lid closed in a cool, dry place (not the fridge); most labels say use within 1 month

Breast milk follows different, longer storage rules than formula, so keep track of which is which when you prep bottles ahead.

Is your baby getting enough?

Whether your baby is breastfed, formula fed or both, the same signs tell you feeding is going well: steady weight gain, plenty of wet and dirty diapers, and a baby who seems content after most feeds. To estimate how much milk babies typically need by age, try the breast milk intake calculator.

For more on the basics of feeding your baby, visit our breastfeeding basics hub.

When to call a doctor or lactation consultant

Call your baby’s doctor if your baby has fewer wet diapers than usual, isn’t gaining weight, vomits often, seems unusually sleepy or hard to wake for feeds, or shows signs of an allergic reaction such as hives, swelling or blood in the stool after starting formula.

See your own doctor if you have a painful, red or hot area on your breast with fever or flu-like symptoms, as this may be mastitis.

A lactation consultant (IBCLC) can help you build a combination feeding plan, choose which feeds to swap, protect or rebuild your supply, and manage bottle preference. Our breastfeeding support page lists where to find help, including free options.