Enter both measurements to continue.
A schematic fit diagram, scaled to your cup size.
Today's size, not a final one
The calculation itself is identical to any other size check — round the underbust for the band, then read the bust-to-band gap for the cup. What's different during pregnancy is how quickly that gap tends to move.
cup difference = round(bust, in) − band
Both the band and cup commonly increase as pregnancy progresses, often starting well before it's visibly obvious, so treat this result as a snapshot rather than a size to commit to for the full nine months.
Through the trimesters
What tends to change, and when
Tenderness and early growth
Some of the earliest changes are sensitivity and a small increase in cup size, before the band typically shifts much.
Band starts to follow
As the ribcage expands to accommodate breathing changes, the band measurement often needs to grow alongside the cup.
Continued cup growth
Cup size frequently keeps increasing as the body prepares for nursing, sometimes needing a size check close to the due date.
Re-measure when it feels off
A bra that starts digging in, riding up, or feeling loose is a better signal to re-measure than any fixed schedule.
Questions
Pregnancy sizing FAQs
Both band and cup can increase, often starting in the first trimester, though the amount and timing vary widely from person to person.
Roughly once a trimester is a reasonable rhythm, or sooner if a bra starts to feel noticeably tight or uncomfortable.
Maternity bras typically use stretchier fabric, wider bands, and sometimes extra hooks or a stretch panel to accommodate ongoing change.
Many people find soft-cup or wire-free styles more comfortable as the chest changes shape, though this is a personal comfort choice rather than a fixed rule.
Yes — this tool covers clothing sizing only. Any pain, rapid change, or health concern is worth discussing with a doctor or midwife.
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