Diablo 3: Effective Health

What is Effective Health?

Effective Health (EH) is how much damage in relation to mitigation a player can take before dying. For example, say I have 1000 health and no armor and thus, no mitigation. Then lets say, I get attacked for 500 damage an attack. I can take two attacks before I die.

 Now, lets say I have 1000 health and 50% damage reduction from armor. Now I only take half as much damage, at 250 damage. It takes four attacks before I die. My Effective Health is 2000, because I am taking as much damage as I would have as if I had 2000 health and no armor.



How does this play out in Diablo 3?

1. Due to how varied classes work: Armor is the same as resists for damage reduction. Does this mean fire damage is reduced by armor? Yes. All elemental damage can be reduced by armor. Conversely, only physical resist can reduce physical damage taken, so the resist that works closest to armor (and for the sake of the write-up) is Resist All. Why is the system like this? Because Blizzard wanted to apply mitigation evenly between all the classes despite different attributes being the focus. So a Wizard can stack Intelligence like a Barbarian who stacks Strength and get the same survivability benefits. So this leads to the next rule:

2. For the sake of mitigation: 10 Strength = 10 Intelligence = 10 Armor = 1 Resist All
Don’t ignore off-stat gear. Just because because your class does not use strength or intelligence doesn’t mean that piece of gear you’re looking at with the stat on it is worthless.

3. Damage Reduction DOES have diminishing returns, but armor and effective health have a linear relationship.

Damage Reduction is Armor / (Armor + (50 x Monster level))

For example lets say I am in Inferno Act 2. My DR is: 5000 Armor / (5000 Armor + (50 x 62)) = 61.73%. This ratio will never reach one because if it did, that means 100% damage reduction, which is not possible. It can approach 1 infinitely but not reach it. This is diminishing returns.

But what does that mean for effective health?

At 70% damage reduction, you have an EH of 333%
At 75% damage reduction, you have an EH of 400%
At 80% damage reduction, you have an EH of 500%
At 85% damage reduction, you have an EH of 666.67%
At 90% damage reduction, you have an EH of 1000%

Let’s check the equation: EH = Health x (1 + (Armor/(50 x Monster Level))

For example, lets do this with a level 60 mob. I have 30,000 Health and 27,000 Armor:
My Damage Reduction: 27000 / (27000 + (50 x 60)) = 90%
My Effective Health: 30,000 Health x (1+ (27000 Armor / (50 x 60)) = 300,000 EH, which is 1000% of 30000 health.

Each additional point of armor is subject to diminishing returns, but for each extra point of damage reduction is better than the last in relation to effective health.

So how do I calculate my Effective Health?

Armor is just the first part. What about resists? Remember, that works the same as armor for damage reduction divided by 10. So instead of multiplying monster level by 50, we multiply it by 5.  How about Dodge? Lets factor that into EH and we get the grand equation:

EH = Health x (1 + Armor/(50 x Monster Level)) x (1 + (All Resist/(5 x Monster level)) x (1/(1-Dodge %))

Lets say I have 500 Resist All and 30% Dodge on top of my previous stats, with a level 60 mob.

My EH: 30000 HP x (1 + 27000 Armor / (50 x 60)) x (1 + (500 Resist / (5 x 60)) x (1/(1-.30)) = 1142857.143% EH

Conclusion


Effective Health as a consideration is incredibly important in how you view survivability in Inferno mode. While there are diminishing returns, your EH increases as you keep adding more armor and resists, with each subsequent point of damage reduction being even better than the previous one.

References:
Original B.net Forum Post
EH Spreadsheet