What Is Effective Health (EHP)?

The same upgrade, worth fifteen times more

5,000 health. Ten more points of damage reduction.

• At 40% → 50%: you gain 1,667 effective health
• At 80% → 90%: you gain 25,000

Identical-looking upgrade. Fifteen times the value. This is the single least intuitive thing in build maths, and once it clicks it changes how you read every defensive item.

The formula

EHP = health ÷ (1 − damage reduction)

At 40% reduction you take 60% of incoming damage, so your health goes 1 ÷ 0.6 = 1.67 times as far. 5,000 becomes 8,333.

Reduction	Multiplier	EHP at 5,000 health
0%	×1	5,000
50%	×2	10,000
75%	×4	20,000
80%	×5	25,000
90%	×10	50,000
95%	×20	100,000

Stop asking what you block

Here's the reframe that makes all of it obvious.

Don't ask how much you block. Ask how much gets through.

Going from 80% to 90% reduction sounds like a tenth more blocking. It isn't. It halves what reaches you — from 20% down to 10%. Halving incoming damage doubles how long you live, which is exactly what the EHP figure shows.

Going from 40% to 50% only takes the leftover from 60% to 50%. A far smaller proportional change, for the same ten points on the tooltip.

Stacking resistance is really a race to shrink the remainder, and every step makes the next one worth more.

So should you just stack resistance?

No — and this is where the reasoning usually goes wrong in the other direction.

Reduction multiplies your health. With a small health pool there's very little to multiply. The extremes of either stat are both bad:

• Huge health, no reduction → fragile against anything big
• Huge reduction, tiny health pool → still dies to whatever ignores it

The strongest builds move both together. Reduction has increasing returns and health has flat ones, which is an argument for buying both, not for buying one.

Read the percentage, not the armour rating

The calculator wants your final reduction percentage off the character sheet — not a raw armour or resistance number.

Nearly every game converts armour to a percentage through its own curve, and those curves differ enormously. Many have diminishing returns built into the conversion, which partly cancels the increasing returns described here. That's not a contradiction — it's two different mechanisms, and your game's tooltip is the only thing that knows which curve applies.

Entering an armour rating as if it were a percentage produces nonsense.

Why the tool stops at 95%

At 100% reduction, effective health is infinite. That's not a number any game intends, and it's why most games cap resistance somewhere between 70% and 90%.

If your game has a cap, points past it are worth exactly zero — the sharpest possible case of a stat losing value, and worth checking before you chase another 3%.

What this doesn't model

• Dodge and block. Avoidance removes a proportion of hits entirely rather than shrinking every hit — and it's random. Over a long fight it averages out to something like reduction. Over a three-second burst it doesn't, which is precisely when tanks die.
• Separate resistances per damage type
• Flat reduction that subtracts rather than scales
• Shields, absorbs and healing

Like the DPS calculator, this is a comparison tool: run your build, change one stat, see which row wins. The absolute number is the least trustworthy part.

No game data, on purpose

There are no game constants in this calculator. Every number comes from you, which means it can't be wrong about your game — it never claims to know anything about it.

Invented or half-remembered game maths is worse than no tool, because players check.

Print the survivability comparison sheet and change one stat per row.