I am a 23 year old woman who has apparently been in the wrong bra size for most of the last eight years. I started in a 36C in undergrad (wore mostly sports bras in high school, I think, so not sure what cup size I would have been in), then got sized at a 36DD about halfway through college. I'm now in grad school and felt like I was spilling out of the 36DDs, so I took both a ThirdLove and a HarperWilde size quiz and ordered from both. I also used the r/ABraThatFits calculator, which said 36H. ThirdLove sized me at a 38H, but the bra they sent was definitely too big for me in both band and cup. HarperWilde sized me at 36F, and the bras fit perfectly. They are a little uncomfortable until you wash them, which is kinda a bummer since you can't return after you wash, but I haven't wanted to return any of them. I originally bought a Boost and a strapless, and within two weeks had budgeted my paycheck to get two more boosts. I am sending back all my old bras through the HW recycle program, so all I have now (besides sports bras and one Aerie bralette) is HW, and I'm so happy about it. I would recommend using a lingerie bag to wash them, and I always air dry them, but they do feel pretty sturdy and I expect they'll hold up for a while.
As far as fit, I have a rounded/maybe bell shape and fill out the 36F comfortably without overflow or gapping. The gore (connector between two cups) sits flat, the band doesn't dig in (I do have some lines at the end of the day, but that's what happens with any bra for larger breasts and the lines are not red or irritated, just indentations), and with a little bit of initial adjustment, the straps are comfortable without digging in. There's also a connector to make the bands X shaped in the back if you prefer.
Another factor that has me sold on HW is the price. ThirdLove bras are usually >$70 each, which feels crazy to me as a grad student. Prior to these direct to consumer brands, I was wearing (the wrong size) Target bras, which are like $10-20 each. $40 for this bra felt risky when I originally ordered, but now I know that the quality, presumably the durability, and the comfort are well worth it, especially since my 36F size is hard to find in stores. I now own the strapless and 3/4 colors of the Boost. I'm not being paid, sponsored, or rewarded in any way for this review, I just wanted to share because I'm thrilled with this purchase and will be a repeat customer for a long time.