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.
Can you get double weapon proficiency 5e?
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.
Can you stack expertise?
You can get Expertise more than once, but you can never double your proficiency bonus on a roll more than once, as explained in the rules. Selecting the same skill twice would be a waste.
Can a character gain the same proficiency from two different sources?
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.)
Can You double up a skill proficiency ( 5e )?
So according to the basic rules, if a background grants you a redundant proficiency, just pick another that’s appropriate for your character. If only it worked for redundant proficiency with equipment though. Negative. However, the Rogue’s expertise class feature allows you to add 2x your proficiency bonus to two proficiencies of your choice.
Can you add proficiency to two proficiencies in Rogue?
If only it worked for redundant proficiency with equipment though. Negative. However, the Rogue’s expertise class feature allows you to add 2x your proficiency bonus to two proficiencies of your choice. Nnnnope. That said, Rogue gets to pick from a bunch, so just grab another proficiency.
Can a proficiency bonus be multiplied more than once?
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. – D&D Basic Rules V0.1 Chapter 1, P. 7
