This is general sizing guidance, not medical advice. Bodies vary widely in pregnancy. Ask your midwife or health visitor about anything that worries you.
The timeline
| When | What is happening | What to buy |
|---|---|---|
| First trimester | Breasts may feel tender and fuller | Nothing, unless your bras are uncomfortable. Soft, non-wired styles help. |
| Second trimester | Cup and band often increase | One or two maternity bras when your own stop fitting |
| Around 36 to 38 weeks | Close to your early post-birth size | One or two nursing bras, with room in the cup |
| Birth to six weeks | Milk comes in; size fluctuates | Wear what you have; add soft sleep bras if needed |
| Six to eight weeks | Supply settles | Measure again and buy your main set |
| After weaning | Breasts change again | Wait a few months, then re-measure for ordinary bras |
Why not buy everything at once?
Because nobody can predict your feeding size. Some people go up one cup when their milk comes in and some go up three. The band usually comes down as the ribcage settles after birth. A full drawer of bras bought at 30 weeks often fits for a matter of days.
Buying at 36 weeks
- Allow room in the cup. A common rule of thumb is about one cup size. Stretchy upper cups help cover the uncertainty.
- Fit the band on the loosest hook, so you can tighten it as your ribcage draws in.
- Choose non-wired or flexible-wire styles for the early weeks, when fullness changes from hour to hour.
- Buy one or two. Enough for the hospital bag and the first weeks.
The nursing bra calculator applies these allowances to your measurements.
Buying at six to eight weeks
This is the time for a proper fitting, in person or by measuring at home. Measure when your breasts are comfortably full, not straight after a feed. Now is when it makes sense to buy the styles you will live in for months, and to try wired nursing bras if you want them.
Do you need maternity bras as well?
A maternity bra is simply a comfortable, supportive, usually non-wired bra with extra hooks. A nursing bra is the same thing with cups that unclip. You can wear nursing bras throughout pregnancy and save buying two kinds. The only reason not to is cost, if you outgrow them before the baby arrives.
If you are not planning to breastfeed
Your breasts will still change in late pregnancy and after birth. Comfortable, supportive, non-wired bras in your current size are all you need, and you can return to ordinary bras when things settle.
How size typically moves through pregnancy is covered in maternity bra size by trimester, and how many to own in how many nursing bras do you need?
Frequently asked questions
When should I buy my first nursing bra?
Most fitters suggest from about 36 weeks of pregnancy, when your ribcage and breasts are close to the size they will be in the first weeks after birth. Buy one or two at that point.
Can I buy nursing bras early in pregnancy?
You can wear nursing bras as maternity bras from any stage, and many people do. A size bought at 20 weeks is unlikely to fit at 38 weeks or after the birth, so expect to buy again.
When should I get fitted for a nursing bra?
There are two useful points: late pregnancy, for the bras you will wear in the first weeks, and around six to eight weeks after birth, once feeding has settled and your size is more stable.
Work out the size to buy at your stage.
Use the nursing bra calculator →