Originally Posted by coryforsenate
If it's stayed at the same gravity for 3 days, then you're good to go.
Personally, I wait 5+ days with no change in gravity, but that's just me letting the yeast play cleanup.
That's not entirely true. Just because the gravity stabilized doesn't mean your fermentation is not stuck.
With an OG of 51 and a medium range of yeast attenuation at 75% your projected FG should be between 12 and 13.
It really depends on the attenuation of the yeast. This info is usually found on the packet or a chart somewhere.