What happens when you have both resistance and vulnerability to a damage type?

[breckdogg]

Ex. A Tiefling somehow gains vulnerability to fire damage, whether from a magic item, spell, etc.

Would they cancel each other out? Would one come out on top? Or would it be damage rounded down?

Thanks!

[urmom]

Honestly this is something as a DM you would have to figure out. Me personally and in my campaign the vulnerability would be canceled out if they gained resistance, the reason is because with Vulnerability you're taking double the damage and with Resistance you take half. So for me they would just take the damage presented. If you were to do the math it works out the same (ex. 2*2=4 4/2 =2) But again it's totally up to you as the DM. (By all means correct me if there's an actual rule for this)

[Theodoric]

I'd run it as cancelling eachother out, most of the time (there are always things like Elemental Adept, but I'll figure that out once it happens).

What do the already existing spells and abilities that inflict vulnerability say about how they interact with resistance?

[Particle_Man]

According to the phb p. 197, they both apply and resistance is applied first. So they don't quite cancel out in cases where the damage was an odd number.

So your strangely vulnerable tiefling takes a fireball for 25 damage. Resistance kicks in to make it 12 damage (using the "round down" rule from p. 7) and then vulnerability kicks in to make it 24 damage.

So if the damage started as an odd number, the net effect is to reduce the damage by one hit point.

That said, I imagine most DMs don't bother with such niceties and just have them cancel out.

Oh, to add to the mix, any direct reduction of damage (like "take 10 less damage from X") happens before resistance and vulnerability are factored in.

[Man_Over_Game]

According to the phb p. 197, they both apply and resistance is applied first. So they don't quite cancel out in cases where the damage was an odd number.

So your strangely vulnerable tiefling takes a fireball for 25 damage. Resistance kicks in to make it 12 damage (using the "round down" rule from p. 7) and then vulnerability kicks in to make it 24 damage.

So if the damage started as an odd number, the net effect is to reduce the damage by one hit point.

That said, I imagine most DMs don't bother with such niceties and just have them cancel out.

Oh, to add to the mix, any direct reduction of damage (like "take 10 less damage from X") happens before resistance and vulnerability are factored in.

The frustrating part of this is that if Vulnerability was applied first, there'd be no reason for any kind of weird situation dealing with odd numbers.

Vulnerability doubles damage.

Odd numbers x2 = Even numbers.

Even numbers x2 = Even numbers.

In either scenario, using Vulnerability first, then Resistance, would make everything a lot simpler.