EHP Calculator – Effective Health Pool
Compute your character’s Effective Health Pool (EHP) from health, armor, resistances, and damage reduction. Compare builds and see how many hits you can survive.
EHP Calculator
Uses a generic diminishing-returns formula; adjust to match your game if needed.
For buffs like “takes 20% less damage”. Applied after armor/resists.
Incoming Damage Profile
Shares should sum to 100%. The calculator will normalize them if not.
Mitigation from armor is approximated as Armor / (Armor + k).
Results
Effective Health Pool (overall)
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Raw damage you can take from this mix of damage types.
Total Mitigation vs Profile
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Includes armor, resistances, flat and % reductions.
Hits to Die (approx.)
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Based on the typical hit size after mitigation.
Per-Type EHP
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What is Effective Health Pool (EHP)?
In games and RPGs, Effective Health Pool (EHP) is the amount of raw, unmitigated damage your character can take before dying, after accounting for armor, resistances, and other damage reduction. It lets you compare very different defensive setups on a single scale.
For example, 1,000 HP with 50% damage reduction is effectively like having 2,000 HP with no reduction, because every hit is halved. Both builds have an EHP of 2,000 against that damage type.
Formulas used by this EHP calculator
1. Armor mitigation (generic model)
We approximate armor-based physical damage reduction as:
\[ \text{ArmorDR} = \frac{\text{Armor}}{\text{Armor} + k} \]
where \(k\) is a scaling constant you can adjust.
2. Resistances
Physical and elemental resistances are treated as simple percentages:
\[ \text{PhysResDR} = \frac{\text{PhysicalRes\%}}{100}, \quad \text{ElemResDR} = \frac{\text{ElementalRes\%}}{100} \]
3. Combining reductions for each damage type
For physical damage, we combine armor and physical resistance multiplicatively, then apply extra % damage reduction:
\[ \text{DR}_{\text{phys, mult}} = 1 - (1 - \text{ArmorDR}) \cdot (1 - \text{PhysResDR}) \]
\[ \text{DR}_{\text{phys, total}} = 1 - (1 - \text{DR}_{\text{phys, mult}}) \cdot (1 - \text{ExtraDR}) \]
where \(\text{ExtraDR} = \frac{\text{AdditionalDR\%}}{100}\).
For elemental damage, we ignore armor and use elemental resistance plus extra % DR:
\[ \text{DR}_{\text{elem, total}} = 1 - (1 - \text{ElemResDR}) \cdot (1 - \text{ExtraDR}) \]
4. Flat damage reduction per hit
Flat damage reduction is applied after percentage reductions, per hit. For a hit of size \(D\):
\[ D_{\text{after mult}} = D \cdot (1 - \text{DR}_{\text{type,total}}) \]
\[ D_{\text{final}} = \max\left(0,\; D_{\text{after mult}} - \text{FlatDR}\right) \]
5. Effective Health Pool (single damage type)
If we ignore flat reduction and only use multiplicative DR, EHP for a given damage type is:
\[ \text{EHP}_{\text{type}} = \frac{\text{Health}}{1 - \text{DR}_{\text{type,total}}} \]
With flat reduction, EHP depends on hit size. The calculator uses your specified hit size to compute the effective damage per hit and then derives:
\[ \text{HitsToDie} \approx \frac{\text{Health}}{D_{\text{final}}}, \quad \text{EHP} \approx \text{HitsToDie} \times D \]
6. Mixed damage profile (physical + elemental)
Let \(p_{\text{phys}}\) and \(p_{\text{elem}}\) be the fractions of incoming damage that are physical and elemental (they are normalized to sum to 1). The overall effective damage multiplier is:
\[ m_{\text{overall}} = p_{\text{phys}} \cdot m_{\text{phys}} + p_{\text{elem}} \cdot m_{\text{elem}} \]
where \(m_{\text{type}} = \frac{D_{\text{final,type}}}{D_{\text{raw,type}}}\).
\[ \text{EHP}_{\text{overall}} = \frac{\text{Health}}{m_{\text{overall}}} \]
How to use the EHP calculator
- Enter your base health. Use total HP after any flat health bonuses.
- Fill in armor and resistances. If your game has only resistances, leave armor at 0.
- Add flat and % damage reduction. For example, a buff that says “20% less damage taken” is +20% Additional DR.
- Describe the incoming damage. Set a typical hit size and how much is physical vs elemental.
- Click “Calculate EHP”. Read your overall EHP, mitigation, hits to die, and per-type EHP.
Tips for comparing builds with EHP
- Keep the same damage profile when comparing two builds, so you’re changing only your defenses.
- Try different hit sizes: flat reduction is much stronger against many small hits than a few big ones.
- Use per-type EHP to see if you’re over-invested in one defense (e.g., huge physical EHP but weak to magic).
- Remember that some games have caps (e.g., max 75% resistance). Don’t exceed your game’s limits.
Example: comparing two defensive setups
Suppose you’re choosing between:
- Build A: 1,000 HP, 40% physical resistance, 0% elemental resistance.
- Build B: 800 HP, 20% physical resistance, 20% elemental resistance.
Against mostly physical damage, Build A may have higher EHP. Against mixed or elemental-heavy damage, Build B can win despite lower HP.
By plugging both into the calculator with the same damage profile, you can see which build survives more raw damage and more hits.
FAQ
Is this EHP calculator tied to a specific game?
No. It’s designed to be generic. As long as your game’s defenses can be approximated as armor, resistances, and flat/% damage reduction, you can use this tool.
How should I choose the armor constant k?
Many games use a formula similar to Armor / (Armor + k). If you know the exact formula from your game, set k so that the calculator matches a known armor value and its listed damage reduction. Otherwise, treat k as a tuning knob.
Why does EHP change when I change hit size?
Because of flat damage reduction. Subtracting a fixed amount per hit is much more powerful against small hits than large ones, so the effective damage multiplier depends on hit size.
Can I use this for shields, barrier, or temporary HP?
Yes. Add temporary HP or shields to your base health if they apply to the same damage types. If they only apply to some damage, you may want to run separate scenarios.