In a fine dining establishment you should try to tip at least 18%-20%. Fine dining to me means running up a bill of %100 or more for two people. 25% is nice for the server, not obligatory in my book
In a more humble place shoot for at least 15% tip
There is no excuse for not being able to figure out 15%
Just divide your bill by 7 and you have it
Thus a $14 bill (pretax) means a $2 tip for that to reach 15%
Actually, I go the opposite.
The pricier the place, the closer to 15 I stay. The onus is on them for superior service based on prices.
A moderate value joint makes me more generous. There’s no pain in overtipping there.