# Is Ironskin's math wrong?

One of the spells allowed to clerics is Ironskin. While reading it I feel like its math is not correct.

### Ironskin

You gain a +4 enhancement bonus to your existing natural armor bonus (if you do not have a natural armor bonus, you are considered to have an effective natural armor bonus of +0).

This enhancement bonus increases by 1 for every 4 caster levels above 4th, to a maximum of +7 at 15th level.

So it grants you a +4 to +7 bonus to your natural armor bonus; this is good. What does not make sense is that for every 4 caster levels above 4th you gain another +1 but it caps at CL15.

So:

• CL 4–7 is +4
• CL 8–11 is +5
• CL 12–15 is +6
• CL 16–19 is +7

The reason why I chose to have CL4 included is because of the CL15 explanation. I feel like the following is more reasonable as it makes better use of your total caster levels and is more correct about being 4 caster levels above 4th:

• CL 5–8 is +4
• CL 9–12 is +5
• CL 13–16 is +6
• CL 17–20 is +7

So with there being a mistake in the presentation of the spell (I only have access to the online source and can't check the printed version) how should the spell be used?

• Good question! I was looking at this spell the other day and thought capping at 15 was odd given the bump is at levels divisible by 4, but didn't actually work out the math to spot this discrepancy. Commented Oct 14, 2016 at 15:44
• FWIW the printed version (Monster Codex, p. 45) is the same. Commented Oct 14, 2016 at 17:12
• @SevenSidedDie Thanks, at least now I know it wasnt a transfer error Commented Oct 14, 2016 at 17:55

## Yes, it is wrong.

The correct should be every 4 levels after 3rd, the minimum level that you can cast the spell. That formula is followed by many spells that have a scaling bonus.

The scaling should be similar to Barkskin, which is the spell that Ironskin copies. Ironskin has a shorter duration and a stronger effect, but also scales slower and has a personal range:

Barkskin

This enhancement bonus increases by 1 for every three caster levels above 3rd, to a maximum of +5 at 12th level.

Either we follow the minimum caster level (3rd, like barkskin), or the maximum cap would have to be changed to +7 at 16.

The monster codex's errata is not out yet, though.

Corrected writing of Ironskin

The enhancement bonus increases by 1 for every 4 caster levels above 3rd, to a maximum of +7 at 15th.

• 3rd - 6th: +4
• 7th - 10th: +5
• 11th - 14th: +6
• 15th: +7