does it stack?

[khachaturian]

my impression that in an attempt to simplify things, 5e has done away with modifier descriptions for bonuses such as armor, shield, enhancement, deflection, luck, sacred, dodge, natural armor, size, circumstance, etc.

along with this, it seems like everything stacks unless it's two of the same thing- you can't wear two rings of protection, or have two instances of shield of faith up.

so a person with chain mail, a shield, and shield of faith will have an ac 20.

do i have this right?

[akaddk]

I think that's right. Some things don't stack that people sometimes think will stack. Like I don't think Mage Armour or Unarmoured Defence stack. I think there was some argument about Bracers of Defence stacking with things. On the whole, I think most BONUSES stack with each other.

Honestly, with so much ambiguity in the rules, I think we're going to see a comeback of Sage Advice. There's a discussion on the WotC forums about stacking AC benefits to something ridiculous like 35 AC by 7th-level or something and someone came along and broke it down and said hardly any of it stacked. I can't remember the details only that I thought on reading it at the time that 5e is going to create a lot of rules debate and contention at tables with it's vague rules descriptions. I had thought this was something they'd move away from but apparently it's something they embraced intentionally.

[Chaosvii7]

The key behind knowing if something stacks or not is if it's a flat number versus if it's a modifier(as in a number preceded by a plus sign;Shield of faith's +2 is a modifier just like shields are a +2 modifier).

Things that aren't modifiers outright replace the base calculations; Mage Armor and Unarmored Defense replace regular armor calculations.

Things like your buffs stack with each other specifically because they modify a number by adding onto it. You can wear just a shield for +2 AC, but you can wear any kind of armor with that and that AC will increase by 2.