How to Combo Feed: A Guide to Safely Feeding Your Baby Breastmilk and Formula

Learn how to combo feed your baby with both breastmilk and formula, including preparation tips, safe storage, warming guidelines, and how much milk babies typically need.

Combo feeding—giving your baby both breastmilk and formula—can offer flexibility while still providing many of the benefits of breastfeeding. Whether you’re returning to work, navigating supply challenges, or just finding the balance that works best for your family, this guide will walk you through how to safely and confidently combine breastmilk and formula feeding.

What Is Combo Feeding?

Combo feeding (also known as mixed feeding) simply means that your baby gets some feeds from breastmilk and some from infant formula. This can look different for every family—some might breastfeed during the day and offer formula at night, while others might alternate bottles of each.

Should You Mix Breastmilk and Formula in the Same Bottle?

No, it’s best not to mix breastmilk and formula together in the same bottle. Formula must be prepared exactly according to the manufacturer’s instructions to ensure it has the right concentration of nutrients. Mixing it with breastmilk beforehand may alter that balance and could reduce its safety or effectiveness.

Instead:

  • Prepare the formula separately.

  • Offer the breastmilk first (if desired).

  • Offer the formula afterward if the baby is still hungry.

This also helps reduce waste—any leftover breastmilk can often be saved for later (depending on how it was handled), while leftover formula generally needs to be discarded within 1 hour of the start of feeding.

How to Prepare Formula

Follow these steps carefully:

Wash your hands and clean all bottles and nipples thoroughly.

Boil water if your baby is under 3 months old, was born prematurely, or has a compromised immune system. Let it cool to around body temperature (98–100°F or 37°C).

Measure the water into the bottle first, then add the formula powder according to the instructions on the container.

Shake well to fully dissolve the powder.

Use the formula within 1 hour of the start of feeding. Discard any unused portion.

How to Store and Warm Breastmilk

Storing breastmilk:

  • Room temp (up to 77°F/25°C): Up to 4 hours

  • Refrigerator (≤ 40°F/4°C): Up to 4 days

  • Freezer (≤ 0°F/-18°C): 6 months optimal, 12 months acceptable

Defrosting frozen breastmilk:

  • Place in the fridge overnight or run under warm water.

  • Do not microwave breastmilk (hot spots can form and damage milk proteins).

  • Once thawed, use within 24 hours. Do not refreeze.

Warming breastmilk:

  • Warm under running warm water or use a bottle warmer.

  • Swirl gently to mix any separated fat.

How Much Milk Does a Baby Need After One Month?

Once your baby is beyond the newborn stage, feeding becomes more predictable.

Babies 1–4 months:

  • Average intake: 24–32 oz (710–946 mL) per day

  • Divide this across 6–8 feedings: about 3–5 oz (90–150 mL) per feed

Babies 4–6 months:

  • Still consuming about 24–32 oz per day, possibly fewer feeds (5–6 daily)

Babies 6+ months:

  • Solid foods may begin to reduce milk intake

  • Aim for 24 oz/day on average, adjusting based on appetite

Whether you’re offering breastmilk or formula, remember that volume per feed can vary based on the baby’s needs, growth, and feeding frequency. It’s okay if some feeds are larger or smaller.

Tips for Successful Combo Feeding

  • Maintain your milk supply by continuing to pump or breastfeed regularly.

  • Track feedings so you know how much your baby is getting and when.

  • Watch your baby’s cues—look for signs of hunger and fullness rather than sticking strictly to the clock.

  • Communicate with your pediatrician—especially when adjusting volumes or troubleshooting digestion issues.

Final Thoughts

Combo feeding can be a wonderful way to support both your baby’s health and your personal feeding goals. Whether you’re transitioning gradually, combo feeding long-term, or just supplementing occasionally, following safe prep and storage guidelines can make the experience smooth and nourishing for everyone involved.

If you ever need help with bottle refusal, pumping, or adjusting your feeding plan, don’t hesitate to reach out to a lactation consultant who supports combo feeding and can help tailor a plan just for you.