[BUG] Rune’s 25% Armour Increase Has Zero Effect on Damage Reduction - May 25th 2025

Helmet A (base reference): 270 Armour - Results in 24% physical damage reduction

Helmet B (before rune applied): 627 Armour - Results in 33% physical damage reduction

This confirms that 627 Armour = 33% mitigation.

Then a rune is socketed which adds +25% increased Armour, meaning the new armour stat becomes 784.

But the damage reduction % stays at 33%, proving the rune’s bonus is not applied in the mitigation formula.

Expected Behavior:
If the rune was working properly, mitigation should reflect the increase from 627 → 784 armour, a +25% boost.

We already saw: 270 → 627 = +357 armour = +9% mitigation

Now: 627 → 784 = +157 armour = ~44% of the previous increase - So the mitigation should go from 33% → ~37%

The Bug:
When the Greater Resolve Rune is socketed, the character sheet shows the higher armor number (784), but the damage reduction % remains at 33%, meaning the extra 157 armour from the rune is not being factored into the actual mitigation formula.

We expect a 25% armour increase on top of 627 to push mitigation from 33% → ~37% — but no increase occurs.

Expected Behavior:
25% increased Armour from the rune should improve the % of physical damage reduction, especially since previous increases (270 → 627) resulted in a clear gain (24% → 33%).

Going from 627 → 784 should add ~4% more mitigation.

Actual Behavior:
Socketed rune increases total armour visually

No change to damage reduction percentage (remains 33%)

Rune bonus is not included in the mitigation calculation

Impact:
Defensive rune bonuses are broken — builds depending on rune scaling gain no actual survivability.

Misleads players by inflating visible armour but giving no defensive benefit.

Reduces strategic value of rune system entirely in armor-focused setups.

That's not how the armour formula works at all. And no, 627 armour does NOT equal 33% mitigation. It equals 33% mitigation versus a certain size hit.

You have no idea what you are talking about - meanwhile I provided quite substantial replicating material and mathematical data based off of the ingame engines output machine meanwhile you just splatter incoherent assumptions grandstanding as if you are the developer talking about certain size hit (completely irrelevant) - go ingame, and do the analysis yourself, let's not endlessly debate ignorantly with assumptions how the calculations are made.

All I am doing is pointing out the inconsistencies of engine not working on a material increase via the socket - the engine will increase and output that increase solely on the armour modifier except when this case is presented with the rune mechanics. Now please delete your comment as it makes you look like an idiot.

Not to mention, but each and every level, that value becomes less effective (diminishes), iir, vs the next lvl higher mob.

At any rate, at a quick glance, it would seem that you havent calculated 'all' the required info's.

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powerofthegods#1104 wrote:

The Bug:
When the Greater Resolve Rune is socketed, the character sheet shows the higher armor number (784), but the damage reduction % remains at 33%, meaning the extra 157 armour from the rune is not being factored into the actual mitigation formula.

I shall assume that you were using a Greater Iron Rune, since you indicated an increase in your helmet's displayed armour from applying the rune. A Greater Resolve Rune would have added +10 Intelligence when applied to a helmet or other piece of armour.


As others have suggested, armour is not a linear calculation and becomes less and less effective as the relative size of a hit increases.

However, in your example where 627 armour* shows a 33% estimated pdr, expecting close to 36-37% from an armour value approaching 789 would be warranted. I am basing this on the armour calculation from the wiki, which suggests that the armour calculation is expected to be similar to POE1 but with armour having about half of the effectiveness in POE2.

[That estimate would reflect a hit of approximately 134 'raw physical damage,' presumably based upon a hypothetical white mob at your current level.]



I did run a test which checked the resulting calculations when adjusting overall armour both with and without a rune. None of my character, equipment, or rune is the same as your case, however. This character was a level 36 ranger with only one small source of armour scaling (18% increased armour on an amulet).

I used a Lesser Iron Rune (15% increased armour) in my test, not the Greater Rune you applied (though they were released in the same change).

It is certainly possible that a specific rune might exhibit a problem others don't. We saw this for some things when the attribute runes were introduced.



I don't suggest that my test refutes your result, but I did in fact see a small difference in my displayed estimated physical damage reduction (pdr) after socketing the lesser rune into a high-armour helmet.

Further, the estimated pdr for a given total amount of armour agreed whether the rune was present or not. That is, I manipulated the gear on my character to achieve the same total armour rating both with and without the socketed rune.





* Edited just to correct a typo where I referenced 672 armour instead of 627.

"

powerofthegods#1104 wrote:

Helmet A (base reference): 270 Armour - Results in 24% physical damage reduction

Helmet B (before rune applied): 627 Armour - Results in 33% physical damage reduction

This confirms that 627 Armour = 33% mitigation.

You say "quite substantial replicating material and mathematical data", but the very first info you provided simply doesn't add up with the armour formula.

If a character has 24% PDR with 270 armour, with 627 armour it would have ~42% PDR, not 33%. Are you wearing the helmets on different characters (with different level)?

As @MonaHuna#6449 suggests, there is ambiguity about where the OP's provided numbers are coming from and how they relate to their total armour. This makes it difficult to assess what they are seeing.


I'm not trying to give you a hard time, but it makes us question the accuracy of the information you provided and whether there may be a misunderstanding contributing to your concern. Regardless, if you are seeing a substantial change in your total armour, it would be reasonable to expect to see a change in your pdr estimate. If, on the other hand, the change to your total armour is proportionately small, you might not. Keep in mind that GGG tends to truncate most calculations (rounding down).

It's not clear to me from your original message if the armour values you are providing reflect just your helmet or your total armour. These could be the same if the helmet was your only source of armour and you had no other armour scaling.


There is often confusion about what %increased armour / defences means as it applies to a piece of gear. When this modifier is found on a body armour, helmet, gloves, boots, or shield, it is a local modifier that only applies to the armour value of that specific piece of gear. It does not scale your other sources of armour. This is also true for runes and quality on the item.

Your physical damage reduction is shown as an estimate of what the reduction would be for a hypothetical physical hit from a monster at your character's current level. This means that the estimate could change significantly between two characters of different levels with similar armour totals. If your total armour is already very high, further improvement to that estimate may require a lot of additional armour.


Perhaps I am being pedantic, but insulting people who have replied to your post isn't helping. @TemjinGold#1898's post wasn't incorrect and reflected the possibility of there being such a misunderstanding.

Would you mind clarifying:
What is the total armour of your character before and after the rune was socketed?
What is the armour value of the helmet alone before and after the rune was socketed?
Does the helmet have quality or other affixes providing %increased armour?

As I have indicated in both messages, your expectation for an increase in the estimated pdr would be warranted if your total armour increased from 627 to 784. From your description, it sounds like that would be the case if the helmet was your only source of armour.