My new go to bra, day and night. I wear a 36C. I purchased L for day and XL for night. Both fit well for their purpose.  I no longer wear my traditional underwire bra because these are so comfortable. Size L fits snug and holds "them" up just fine, and for a 50 something women, that's quite good. Size XL is a great fit and really comfy for sleeping and casual wear. I purchased a different color in XL to tell the sizes apart from each other so that I could grab and go.

Size up for a more comfortable fit. If you wear size 10/12 US order L, size 14 Us  order XL.
I am 170 lbs, 5'5", 36C. L is my T-shirt size and XL is my sleeping size. Hope this helps.  Oh, by the way, XL is easier to put on.  For L, I step into it and pull it up due to a shoulder I jury.