I've said it before that I think skill proficiencies need a buff, being proficient in a skill grating 10 to 20% chance to succeed in an average DC is to little.
The calculation seems to be the same as in 5e. If you're proficient in a skill you add your proficiency bonus which starts at +2 and goes up as you hit certain level milestones. You also add the relevant skill modifier. So a level 4 18 CHA character proficient in persuasion will get +6 to rolls (a 30% increase in success). At higher levels this will increase further.
