Effective Health Calculator
Enter your health pool and a damage-reduction percentage to get your effective health (EHP) — and see why each point of reduction is worth more the more you stack.
See how far your HP really goes
Enter your health and damage reduction and the effective health calculator returns your EHP — how much raw damage you can absorb before dying.
One damage type
Reduction applies to a single damage type (such as physical armor). Mixed damage and resistance caps are not modeled here.
What is effective health?
The real size of your health bar
Effective health (EHP) is how much raw incoming damage your character can survive once damage reduction is taken into account. A 1000-HP character with 40 % damage reduction does not die after 1000 damage — every hit lands at 60 % strength, so it takes about 1667 damage to bring them down. That 1667 is the effective health. The effective health calculator turns two numbers, your raw health and the fraction of damage you mitigate (from armor, resistances, or a defensive buff), into the size of your health bar as the enemy actually experiences it. It is the number behind every "is more armor or more HP better?" debate in ARPGs, MOBAs, MMOs, and shooters.
Enter a health pool and a damage-reduction percentage to get your effective health in EHP instantly.
Effective health is your raw health divided by the share of damage that still gets through after reduction — that is, one minus the reduction expressed as a fraction.
EHP = health / (1 − reduction)Reduction enters the formula as a fraction, so 40 % becomes 0.40 and the divisor is 1 − 0.40 = 0.60. Because you divide by that shrinking number, the effective health climbs faster and faster as reduction rises — the curve is 1 / (1 − r), not a straight line. At 0 % reduction the EHP equals your raw health; at 50 % it doubles; at 75 % it quadruples.
Suppose your character has 1000 health and 40 % damage reduction from armor.
Turn the reduction into a fraction
40 % becomes 0.40 — the share of each hit that is blocked.
Find the share that gets through
1 − 0.40 = 0.60 — sixty percent of every hit still lands.
Divide the health by that share
1000 ÷ 0.60 ≈ 1666.67 EHP — the raw damage you can absorb before dying.
Your effective health is the honest size of your health bar against one damage type. The key insight is the shape of the 1 / (1 − reduction) curve: each additional percentage point of reduction is worth more than the last. Going from 0 % to 10 % reduction multiplies your EHP by about 1.11, but going from 80 % to 90 % multiplies it by 2 — the same ten points doubles your survivability. This is why stacking resistance "scales" so well in many games: every flat point of reduction protects a larger and larger health pool. It also explains the classic build trade-off. Raw health raises EHP in a straight line (10 % more HP is always 10 % more EHP), while reduction raises it on the steepening curve, so once you already have some armor, another chunk of reduction usually buys more survivability than the equivalent investment in flat health. Compare two builds by computing the EHP of each rather than eyeballing the raw numbers — the bigger EHP wins, regardless of how the points are split.
The formula is exact, but it models a deliberately simple situation.
Single damage type, no caps, reduction below 100 %
This calculator handles one damage type at a time, so a character with different physical and magical reduction needs a separate EHP for each. It also ignores any in-game cap on resistance and any source of healing or shields on top of the health bar. Reduction must stay below 100 %: at 100 % the divisor becomes zero and effective health would be infinite, which no real game allows, so the calculator accepts up to 99 %.