Maternity Bra Calculator
Pregnancy changes your body on a schedule — and your bra size changes with it. The Maternity Bra Calculator works out your current size from your measurements, then adds stage-specific guidance: what usually changes in each trimester, what to look for in a nursing bra, and when to measure again instead of buying more bras.
Your Measurements and Stage
Sizes on this page are estimates. Sizing varies by brand and style, so always check the brand’s own size chart and try on before you buy. Nothing here is medical advice.
What changes, stage by stage
Early pregnancy
Change is often gradual: tenderness and slight fullness are common, but many people stay in their usual size for a while. A soft, stretchy bra in your current size is usually enough.
Second trimester
The rib cage expands, so the band often feels tighter before the cups do. A band extender is a cheap bridge — it buys room without a new size. If cups start spilling, go up a cup on the same band.
Third trimester
Fullness is usually at its peak, and size can shift again quickly. This is the best time to buy nursing bras if you plan to nurse, because you are closest to your nursing size.
Postpartum and nursing
Size often settles over several weeks, and fullness changes through the day with feeding. Fit to your fullest (pre-feed) fullness, prefer drop cups and flexible cups, and re-measure once things feel stable.
Choosing a nursing bra
Three features matter most. One-handed drop cups or clips: you will often have one hand free, not two. Flexible cups: stretch lace or soft cups adapt as fullness changes through the day, while rigid moulded cups cannot. A comfortable band: you will sit for long feeds, so a band that digs will bother you far more than it used to. Fit the band snug and level, as with any bra — comfort does not mean loose.
When to measure again
Measure again each trimester, after birth, and whenever your bras stop fitting comfortably. Do not stock up on many bras at any one stage — buy one or two, then re-check. Your size is a moving target during pregnancy, and the cheapest mistake is a drawer full of the wrong size.
A simple buying timeline
Early pregnancy: buy nothing special yet unless you are uncomfortable — a soft, stretchy bra in your current size usually covers this stage. Second trimester: add a band extender before you buy a new size; it is the cheapest fix for a tightening band. Third trimester: buy one or two nursing bras if you plan to nurse, fitted to your current size. After birth: wait until your size feels stable for a couple of weeks before stocking up, and re-measure at that point.
The expensive mistake is buying five bras at one stage. Sizes move during pregnancy, and a drawer full of the wrong size helps no one. One or two well-fitting bras per stage, re-measured at each step, costs less and feels better.
Frequently Asked Questions
When should I buy a maternity or nursing bra?
Late in pregnancy is usually the best time for nursing bras, because size changes most in the third trimester and again after birth. For everyday comfort earlier on, a soft, flexible bra in your current size — or one band up — often works until then.
Should I measure differently while pregnant?
No — the measurements are the same: snug underbust and fullest bust. The difference is timing: measure again each trimester and after birth, because the numbers move.
What makes a nursing bra different?
Drop cups or clips that open one-handed for feeding, flexible cups that adapt as fullness changes through the day, and a comfortable band that does not dig when you are sitting for long feeds.
Will my size go back after pregnancy?
Often it settles close to — but not always exactly — your pre-pregnancy size. Weight, breastfeeding and time all play a part. Re-measure once things feel stable rather than assuming your old size.
Is underwire safe during pregnancy and nursing?
Comfort is the guide. Some people find underwire uncomfortable as fullness changes, and a rigid wire that presses on tissue is never a good fit. Many people prefer wireless or flexible-wire styles while nursing. If anything hurts, change the bra.