Math Behind Maximum Resistances

I currently have 89% fire, cold, and light res on my build. I'm trying to determine the benefits of going from 88% to 89%, then from 89% to 90%. Does anyone understand the math behind this and could you please explain to me? Thanks so much!

Assuming you have a build where the max res is 90%, for every 100 points of ele damage, 12 will get through at 88%, given no other mitigations. If you go from 88 to 89%, only 11 will get through. So you are reducing your ele damage taken by 1/12 or about 8%, all other things being equal.

Just consider the difference in damage taken between two numbers.

For example:

At 0% resistance you take 100% damage. At 50% res you cut the damage in half so only 50% damage taken compared to 0 resis. At 75% res you cut the damage in half again compared to 50% as you only take 25% instead of 50%. Going from 75% to 80% means 20% less damage as you only take 20% now, not 25%. Then going from 80% to 90% you actually cut the damage in half again as you only take 10% instead of 20 and so on. Generally the more resis you already have the more impact every single point gets.

They pretty much got it. 88→89 is taking 1/12 less damage (8.3%). 89→90 is taking 1/11 less damage (9.1%).

The damage you are already mitigating should be ignored in the calculations. It’s already inherently factored in.

Thanks guys appreciate the guidance! :)