Effective HP with Damage Reduction & Dodge Calculator

Understanding the effective HP with dodge calculator — concept and principle

Effective HP (EHP) answers a simple question: how much raw incoming damage can you absorb before dying? Health alone does not tell you, because damage reduction from armor or resistances and a chance to dodge attacks entirely both stretch that health further. This calculator combines HP, a percentage damage reduction and a dodge chance into one average EHP figure, so you can compare defensive stats on a single scale.

Dodge and reduction multiply: only 56 of every 100 damage gets through on average.

How it is calculated

Effective HP = HP ÷ ((1 − DR) × (1 − dodge)), with DR and dodge as decimals.

The term (1 − DR) is the share of a hit that gets through after reduction, and (1 − dodge) is the share of hits that land at all. Their product is the fraction of incoming raw damage you actually take on average. A full block that negates a hit can be entered as part of the dodge chance.

The principle

If you take only a fraction f of incoming damage, your health lasts 1 ÷ f times as long, so EHP = HP ÷ f. Reduction and dodge are independent layers: first a hit must avoid your dodge, then the part that lands is reduced. Independent layers multiply rather than add, so 30% reduction and 20% dodge let through 0.7 × 0.8 = 56% of damage, not 50%. This multiplication is also why stacking any single defensive stat shows rising returns in EHP: moving from 80% to 90% reduction doubles EHP.

Worked example

Inputs: HP 5,000, damage reduction 30%, dodge 20%.
Damage that gets through: (1 − 0.30) × (1 − 0.20) = 0.7 × 0.8 = 0.56.
Effective HP = 5,000 ÷ 0.56 = 8,928.57 (8,928.571429).

Each point is the calculator re-run with only “HP” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

HP	Effective HP
1,250	2,232.142857
2,500	4,464.285714
3,750	6,696.428571
5,000	8,928.571429
6,250	11,160.71429
7,500	13,392.85714
10,000	17,857.14286

How to read the result

Here you survive about 79% more raw damage than your HP suggests. To compare upgrades, calculate EHP for each option: adding 10% reduction (to 40%) gives 5,000 ÷ (0.6 × 0.8) ≈ 10,417, while adding 1,000 HP gives 10,714. The bigger number wins against the damage type the stats apply to. Dodge is an average: over a short fight you may dodge nothing or everything, so builds that rely on dodge feel swingier than reduction builds with the same EHP.

Common mistakes

Adding reduction and dodge percentages instead of multiplying the remaining fractions.
Treating EHP as protection from every damage type; armor-based reduction may not apply to magic or true damage.
Forgetting healing, shields and regeneration, which add survivability outside this formula.

Keep in mind: The result is an average assuming independent dodge rolls and a constant reduction. Games with dodge caps, entropy-based evasion, damage over time or one-shot mechanics behave differently, so check how your game applies each stat.

Frequently asked questions

Why does stacking damage reduction get stronger?

EHP depends on 1 ÷ (1 − DR); as DR approaches 100%, the denominator shrinks toward zero, so each extra percent matters more. Most games cap it for that reason.

Is dodge as good as damage reduction with the same percentage?

On average, yes; 20% of either multiplies EHP by 1.25. Dodge has higher variance.

How do I include armor from an armor ÷ (armor + K) formula?

Convert it to a reduction percentage first, then enter that value as DR.

Sources: Sheldon M. Ross, A First Course in Probability (independent events and expected value)

Checked 8 Nov 2026. Official league / federation formulas where they exist; widely used community formulas otherwise. For fun and analysis — not betting advice.

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