They do NOT stack. If you have Expertise, taking a Feat to allow you to add double your proficiency bonus does not let you quadruple your Proficiency Bonus. Jeremy Crawford (Sage Advice) answered this specifically.
What happens if you have double proficiency 5e?
“You gain expertise with that skill, which means your proficiency bonus is doubled for any ability check you make with it.” Twice Proficiency allows you to apply double proficiency to a skill or tool under a specific situation, even if you are not already proficient in that skill or tool.
How high can proficiency bonus get?
The character sheet on DDB adds it automatically to these modifiers and values, so you don’t have to worry about that. Proficiency bonus starts at +2 and increases every 4 levels to a max of +6 (for players, monsters have a proficiency bonus too).
Can a proficiency bonus be added more than once?
Occasionally, your proficiency bonus might be modified (doubled or halved, for example) before you apply it. If a circumstance suggests that your proficiency bonus applies more than once to the same roll or that it should be multiplied more than once, you nevertheless add it only once, multiply it only once, and halve it only once.
Can a rogue double their proficiency bonus at Level 6?
– D&D Basic Rules V0.1 Chapter 3, P. 27 While not allowing proficiency bonuses to be counted more than once, expertise allows a Rogue to double the benefit of their proficiency bonus to two skills (or thieves’ tools) at level 1 and again at level 6. In the Backgrounds section of the Basic Rules & PHB, the following rule is listed:
Can a character choose two proficiencies from the same skill?
In the Backgrounds section of the Basic Rules & PHB, the following rule is listed: If a character would gain the same proficiency from two different sources, he or she can choose a different proficiency of the same kind (skill or tool) instead. (Note that, while unclear, this rule may only apply to background proficiencies.)
How do proficiencies with one thing from multiple different sources stack?
Do proficiencies with one thing from multiple different sources stack? In D&D 5e it is possible for a character to receive proficiency in the same skill, tool, weapon and/or armor more than once via Class, Race, and/or Background. Do any of these proficiencies stack, thereby allowing a character to receive their proficiency bonus more than once?
