5 to 7 standard size cup/mugs per day. I drink it black, no sugar or creamer. I used to worry about the health effects. But studies like this [1] suggest that it their might increased health benefits up to about 5 cups a day. So I have decided to enjoy my coffee and just keep an eye on it to not interfere with sleep.

[1] https://academic.oup.com/aje/article/182/12/1010/2195423/Ass...