I've noticed that for full table magic users (spells going up to 9th level), a new level spell slot opens up every two levels, it goes like this up until level 17 where it caps off at that point assumedly since there are no 10th level spell slots to be gained on levels 19 and 20.
It looks like there's some math going on behind the scenes here so I was wondering if anyone has had a crack at this and figured how similar tables could be constructed for homebrew content?
Context: I'm brewing together a system for a sorcerer which requires them to keep using spells to discharge their inner magic on a daily basis or risk their magic overflowing and potentially causing hilarious terrible things to happen to them and/or their party. I've got the capacity and mechanics down I just now need to figure out a way to keep the discharge effort consistent with the sorcerer gaining more and higher level spells as they level up.
To clear up some confusion I'll give an example situation.
Let's make it relatively simple and say I want a sorcerer to spend half of his magic every day or else he catches fire.
For 1st and 2nd level it's pretty straightforward:
- 1st level – player has two 1st level slots, has to use one to achieve
50% - 2nd level – player has three 1st level slots, has to use two to
achieve at least 50% - 3rd level – this is where the problems start, player now has four 1st
level slots and two 2nd level slots, using two 1st level spells and
one 2nd level spell would be 50%, but what if they cast four 1st
level spells, would that be the same? Is a 2nd level spell slot really twice as good as a 1st level spell slot? What about 3rd level spell slot?
I was looking for a mathematical formula which would detail the growth in slot amount and level to then perhaps somehow be able to extract an intrinsic value of a spell slot level, which would then allow me to assign a numerical figure to a casters spell budget, which I would be able to then apply percentage based goals upon.
Best Answer
You should read the section Variant: Spell Points, starting on page 288 of the DMG.
The easiest would be to just use the variant, as the half of all spell points is well defined. As the character is already a sorcerer (with Flexible Casting from level 2), changing completely to the variant will only simplify things.
If for some reason you wish to use spell slots, you could use the table on that same page that defines the "point cost" of a spell of a given level. You add up all his spell slots (maybe sorcery points too) and compare the value of used spell slots to that. You (or your player) will still need to keep track of the spell-point-equivalent of slots yet spent, though.