Indeed, but they do say "The calculation result is only a starting point. A professional fitting or trying on bras to see which sizes work best is recommended."
they don't loosen over the day, but your body does and makes it feel tighter toward the end of the day. more like a ring than a shoe
they do loosen over time. most bras have 3-4 hooks, you start on the loosest and the only reasons you use the tightest is you got a bad fit or it's near time to throw it out
* And if you're buxom? Forget it. You have to own an array or be in pain.*
If you are buxom enough, you might not be able to afford or find an array of bras. If I buy in my size - generally around an H cup - bras easily range from $80-$120 each. I always have to buy a specialty bra. I had never found my size in an actual store in the US: I had to move to Europe for that.
All that said: Once I was able to find bras in my size, I did find that many are well-made, they fit and aren't rubbing nor digging in, and wearing them through the day hasn't really been an issue. At least, until they are wearing out and needing replaced.
My wife is a 28J in US sizes. Panache is your friend. Amazon Wardrobe will let you get up to 6 at a time and return whatever doesn't fit right. At least the situation is improving--she used to have to get custom only.
