How much tanning does it take to get wrinkles and cancer?

No formula: This depends on your genetic tendencies and predisposition as well as the frequency of tanning and the severity of the burns. Your skin color will have a great influence.

Can't quanitfy: Tanning causes wrinkles and skin cancer... Neither of which you want! avoid it and always use sun block when you're in the sun.

A good amount, but..: Generally, these types of adverse events are associated with long term sun exposure over time, however, genetics and other factors play a part as well and can accelerate this. The best thing to do is always wear a good sunscreen containing uva and uvb protection and to wear a hat when in the sun. Prevention here is the key and everyday makes a difference.