Are you the one who can't start a day without coffee and keep consuming it through the day to able to function more efficiently?
According to docs, experts, google, quora etc... 4 cup of coffee seems OK for most healthy inviduals. That makes around 400mg of caffeine. That's the daily safety limit for 'adults only' by the way.
Also women who is pregnant or trying to be, should see their docs for updated levels. Also consider if you should cut it down if you take some certain medicines on regular basis.
Coffee is fun when you don't abuse it like i do. To get most of it, do not exceed the limits that your body requires according to your mental or physical condition. Consider checking your limits if you having some of these after you enjoy your last coffee of the day:
Insomnia
Irritability
Nervousness
Restlessness
Frequent urination
Fast heartbeat
Enjoy your coffee responsibly. Have the best you can. Focus on quality not on quantity.
Thanks for your time.