How do ability score improvements improve modifiers?

Question

First time player in a group figuring out things as we all go.

I just hit level four as a Ranger, and I get to improve one ability score of my choice by 2, or I can increase two ability scores of my choice by 1.

My first thought was Strength, as I've been rocking a score of 11 with a mod of +0 so far. But I read that Rangers use (wisdom mod + 10) for their spell casting modifier. Currently my wisdom is 13, with a mod of +1. If I increase either STR or WIS, will the modifier increase as well? How and why?

A Monk in our party went from 9 CON to 11 during their ability score improvement, and by doing so their modifier went from −1 to 0.

We're all pretty new, so between eight people we're currently sharing one book, and all trying to locate our own copies for later campaigns. That's making it… inefficient for us to learn these things quickly.

Answer 1

Typically you'll be able to make an improvement to your stats at level 4, 8, 12, 16 and 19.

The ability modifier is based on your ability score. If you look on p.13 of the PHB you'll see the chart.

\begin{array}{cc} \text{Score} & \text{Modifier} \\ \hline 1 & -5\\ 2\text{–}3 & -4\\ 4\text{–}5 & -3\\ 6\text{–}7 & -2\\ 8\text{–}9 & -1\\ 10\text{–}11 & +0\\ 12\text{–}13 & +1\\ 14\text{–}15 & +2\\ 16\text{–}17 & +3\\ 18\text{–}19 & +4\\ 20 & +5\\ \vdots & \vdots \end{array}

Answer 2

If you increase Strength 11 to 12 and Wisdom 13 to 14, both of those modifiers will increase (to +1 and +2), in accordance with the chart Francisco posted.

Due to how modifiers work there is effectively a "breakpoint" every 2 points of an ability score. The difference between a Strength of 10 and one of 11 is very slight, but the difference between 11 and 12 is significant.

In general, I try to even out my ability scores by making all my odds even, at least in the ones you care about (Charisma and Intelligence might not be too useful for your character).

Answer 3

Essentially, you have two ability points you can allocate however you choose. You can allocate two points to the same stat, or 1 point each to two stats. Once you've allocated your ability points, you then recalculate your modifiers for any stats that have changed. The formula is \$\text{floor}(\frac{\text{stat} - 10}{2})\$.

In your case you've described two stats that you are considering bumping. If allocate one point to STR and one point to WIS, your socres with them go from 11 to 12 and 13 to 14 respectively. This will bump your modifier on each of them, from 0 to 1 and 1 to 2 respectively.

You could also allocate both points to either strength or wisdom, but as you round modifiers down, this does not give you any additional bonus.

Answer 4

The simplest way to calculate an ability score's modifier is to subtract 10 from it, then divide it by 2 and round down. For example, if you have a INT of 15, 15-10=5. 5/2 = 2.5, which is 2 rounded down. That means that you have a +2 intelligence modifier. If you don't feel like doing math, they also have a chart in the players handbook. And if you increase a stat that is an even number, like if your CHA was 12, it still can be useful to increase them. Then the next time you want to increase CHA, its modifier will go up.

Answer 5

You get +1 to the modifier at every even total score number

If you are only concerned about Ability Score Improvement (i.e. leveling up rather than character creation) you don't need to worry about the PHB table or anything else complicated. Every time you reach a new even number, you get +1 to your modifier. Increasing to an odd number does nothing.

Answer 6

More or less a "pay me now or pay me later" question. If you want to see immediate benefits, split the adds as others have suggested. A +1/+1 bumps Str and Wis now.

Just be aware that your next level which yields a stat bump might feel like a drought in comparison as one more point in each stat will yield nada (12 to 13 and 14 to 15 yields nothing). It's a step function, not a linear one.

Choose the stat adds that best fit what you want to be able to do more of now and live with the consequences.