90% on my release day XS while my wife is at 100% still. It's within the specified limits.
However, my 7 did go from 100% to 84% one day overnight. The estimate is just that.
How much it degrades depends on usage but a huge factor is heat. Battery chemistry does not like being hot when charging and this can damage the cells. I always topped up my battery (not such a good idea) and I keep it in my pocket so the battery is always at body temprature (also bad). While the wife keeps hers on her desk or in a bag so around 10 degrees lower.
If you've ever done what ive done and left it in a hot car, wrapped up in your clothes in a gym locker while accidentatly running Sat Nav apps that roast the thing then that would damage the cells.
To maximize battery life keep it cool when charging. Dont leave it in the sun, deffinetly not while charging (done that too).
But if you upgrade every year than dont give 2 f's and just use it, your getting rid before it drops too much anyway.