This plan assumes breastfeeding is established — typically around six to eight weeks [6] [2] — and you want to add formula while keeping some breastfeeding. If you are supplementing a newborn on medical advice, follow your care team's plan instead; the principles below still apply.
Give one bottle of formula at the chosen feed. The NHS suggests offering the first bottles when your baby is relaxed and not very hungry, and that it may help if someone else gives them so your baby is not next to you smelling your milk [1].
Use paced feeding: hold your baby fairly upright, keep the bottle near horizontal so milk does not pour, and pause every few minutes. Let your baby decide when to stop; the CDC's guidance is that babies "generally take what they need at each feeding and stop eating when full" [3].
If your breasts feel full at the skipped feed, express just enough for comfort rather than a full pumping session — a full session tells your body to keep making that feed's milk [6].
If your baby is taking the bottle and your breasts have settled, you can either stay at one bottle a day or replace a second feed, again waiting several days before the next change [1] [6]. Do not change two things at once.
By now you have a rhythm. Check the things that matter:
If you are away for a feed you want to protect — back at work, for example — express at that time instead of skipping it. Expressing releases prolactin, which stimulates milk production [1]. Expressed milk can go in a bottle for the next day.
Reducing breastfeeds gradually gives your body time to lower production without engorgement [6]. Expect a few days of fullness after each dropped feed. Sudden stopping is what causes blocked ducts and mastitis; slow change avoids it.
Prepared formula must be used within two hours of preparation and within one hour of starting a feed; anything left after a feed is thrown away, because saliva in the bottle lets bacteria grow [4]. If you make a bottle and do not use it within two hours, refrigerate it immediately and use within 24 hours [4].
Replace one breastfeed a day with a bottle of formula, given when your baby is calm and ideally by someone else. Use a slow-flow teat and paced feeding. Keep that pattern for three to five days before replacing a second feed.
The same way as earlier — one feed at a time — but at six months you are also starting solids, so change only one thing at a time. Replace a daytime breastfeed with formula first, give it a week, then start solids, or the other way round.
Whichever feed you most want to hand over. Many families choose the late-evening feed so a partner can give it and the breastfeeding parent can sleep, and keep the morning breastfeed because supply is usually highest then.
Follow the amounts on the tin for your baby's age and weight and let your baby stop when full. The CDC notes most formula-fed newborns take 1–2 oz every 2–3 hours in the first days and settle to roughly every 3–4 hours in the following weeks.