Question: This is a mechanics question pertaining to the maximum allowed damage for the Paladin's *Divine Smite* ability.

> 
> **Divine Smite:** ...you can expend one [Spell Slot] to deal Radiant damage in addition to weapon damage. The extra damage is 2d8 for a
>  1st level slot, plus 1d8 for each spell level higher than 1st, to a
>  maximum of 5d8....
> 
> 
> 

**"...to a maximum of 5d8..."** is the part I'm having issues with figuring out how to rule.

Can the *extra* damage, beyond the 2d8 for filling a 1st level slot with the ability, be up to 5d8? Which would require a (Multiclass gained) spell slot of 6th level to add an extra 5d8 to the attack, making it 7d8 total (The default 2d8 + the maximum allowed extra of 5d8). *Or*, are the rules saying that the total allowed maximum damage can't exceed 5d8 total; which would only take a 4th level spell slot to add a max of 3d8 to the default 2d8?

2d8 + 3d8 = "to a maximum of 5d8" damage total?  

2d8 + "to a maximum of 5d8" extra total = 7d8 ?

My guess is the first choice, since without Multiclassing a Paladin can never have more than 5th level spell slots and could never have the 6th level slot required to add 5d8 to the attack. My PC differs though.

Answer: 
A compelling argument can be made for either case. Using the total maximum as 5d8 best mirrors how other maximums are written throughout the book. Take, for example, the description of falling damage:

> 
> At the end of a fall, a creature takes 1d6 bludgeoning damage for every 10 feet it fell, to a maximum of 20d6. The creature lands prone, unless it avoids taking damage from the fall. 
> 
> 
> 

*Player's Handbook*, 183

And the "At Higher Levels" of "Hail of Thorns":

> 
> If you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d10 for each slot level above 1st (to a maximum of 6d10).
> 
> 
> 

*Player's Handbook*, 249

Both of these examples use "Some amount of damage, up to some maximum amount of damage". If we assume the goal was to write all maximums in the same way, then it makes sense to assume that the *total maximum damage* is 5d8. 

However, since it wasn't clear, I asked Jeremy Crawford on Twitter:

[Divine Smite: Total maximum is 5d8, or additional spell lvl damage is 5d8? (Can I use a 6th level spell to get 2d8 + 5d8?)](https://twitter.com/GamerJosh/status/568816437047001089)

I will update when (if?) I get a response.
I've always seen it as being the additional damage beyond the 2d8 that is capped at 5d8. For example, a 20th level paladin has up to 5th level spell slots. As written, the damage progression is thus:
1st level slot - 2d8,
2nd level slot - 2d8 +1d8, 
3rd level slot - 2d8 +2d8, 
4th level slot - 2d8 +3d8,
5th level slot - 2d8 +4d8,

Why wouldn't they get to use their 5th level slots? I've always ruled at my own table that the 5d8 limit was for the bonus damage, meaning you can spend up to a 6th level on Smite, but nothing higher (For if you multiclass).