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How does damage mitigation work on a portal? I heard that links and shields make it sturdier and harder to take down, but exactly what's the math behind this?

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I've updated the answer with one important thing about old shields for people, who played at that time. Be sure to check it out! –  Qwerty Jan 11 '14 at 2:04

2 Answers 2

up vote 25 down vote accepted

The mitigation stacks additively and its damage reduction is hard-capped at 95%.
1 mitigation = 1% reduced damage. The mitigation can go over 95, but the extra damage reduction won't apply. Apart from mitigation, a shield has a mysterious property called Stickiness. It is said, that it might affect the destructibility of a deployed shield.

Shield Type         Mitigation  Stickiness
Common shield       30          0
Rare shield         40          150k
Very Rare shield    60          450k
Very Rare "AXA"     70          800k

Portal defense boost based on number of links

A portal with 4 VR shields and with 10 links has 66 100 180 260 300 mitigation, BUT reduces only 95% damage. The extra shields have only the meaning of reserves, when some get destroyed.
It is wise to support shielded portal's defense with links.

The % damage reduction in action

An L8 burster with 2700 damage will do:
*Take a closer look at the defense effect of 80-95%

shield type  defense     damage
-            0%          2700
CS           30%         1890
RS           40%         1620
VRS          60%         1080
AXA          70%         810
RS + RS      80%         540
VRS + CS     90%         270   (same as 3x CS)
VRS + RS     95%         135   (same as 2x CS + RS)

damage reduction effectiveness

I am leaving the following only for historical reasons

first version

# IMPORTANT! # for old players

If you are an old player and you don't use shields much or you didn't play long time for some reason, it may happen that you will have OLD + NEW shields in your inventory. Don't know why it works like that, but if you drop all the shields of same rarity and pick them up again, they will get renewed.
C: 6->10, R: 8->20, VR: 10->30
*do not bother yourself with common shields though, it is only worthy for R and VR S.

EDIT 1 (7 Mar 2014)

The shield strength changed once again, from 10,20,30 to 20,30,50. As far as I can tell, all old shields are renewed automatically without the need of dropping them. I am leaving the hint for historical reasons.

EDIT 2 (3 Jun 2014)

New shield strength :) - from 20,30,50 to 30,40,60. All shields are renewed automatically. Already deployed shields remain with old stats.

EDIT 3 (21 Dec 2014)

New shield type was introduced as a result of sponsorship deal with the international investment banking firm AXA. The so called AXA Shield is very rare and its mitigation is 70. More reading here...

EDIT 4 (4 Feb 2015)

Significantly increased values for stickiness started to show for newly placed shields in the JSON answer in intel. (Reddit: Shield stickiness gone mad in IITC.)

Shield Type         Old   New
Common shield       30    0
Rare shield         40    150000
Very Rare shield    60    450000
Very Rare "AXA"     70    800000
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Nice! Thanks for the updated answer. –  Stupid.Fat.Cat Oct 7 '13 at 1:12
Just wanted to point out that this means that a single link is more powerful than a Common Portal Shield. Adding two links is the same as a Very Rare Shield. A couple of links is a very powerful mitigation strategy. –  womp Jan 13 '14 at 1:17
@womp: while links are still a powerful mitigation strategy (they won't pop off until there's less than 3 resonators remaining on the portal), the shield mitigation edits since your comment make it no longer true that a single link is more powerful than common shields or that two links are the same as a very rare. As of the 3 Jun 2014 shield mitigation changes, a common is about equal to the first two links, and it takes 12+ links to reach the mitigation level of a very rare shield. –  iammichael Jul 2 '14 at 16:57
@RoryAlsop Yes, they are only a bit stronger. I updated the answer. –  Qwerty Dec 21 '14 at 15:06

Shields mitigations are :

  • common shield : 10
  • rare shield : 20
  • very rare shield : 30

The mitigation of the shields is a percentage of absorption of damages. A (common) shield with a mitigation of 10 will absorb 10% of the damages made by the buster. A second (common) shield with mitigation 10 will catch 10% of the remaining damages.

For example, let's imagine a burster making 100 of damages on a resonator. First common shield will absorb 10% so damages will be reduced to 90. A second common shield will absorb 10% of the 90 damages and will reduce damages to 81...

In the worst/better case with 4 very rare shields mitigation 30, a burster making 100 damages will be reduced to 24.

To compute the total mitigation of shields on a portal you have to just multiply the percentages. A very rare shield will eat 30%, to compute the effects you'll have to do X - (X * 30 / 100) that will reduce to X * 0.7. So a very rare shield is equal to a 0.7 factor applied on the burster's damage, a rare shield is equal to 0.8 and a common to 0.9.

So the way of computing shield mitigation is :


To that, you have to add a defense mitigation made by links. The formula seems to be :


where e is the mathematical constant.

This will give you another mitigation to "add" (multiply) to the shield one to obtain final mitigation.

Then to compute the damages the formula is :

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Thank you so much for this, I'm going to be trying to min-max portal defenses with my resources. –  Stupid.Fat.Cat Jun 18 '13 at 3:22
I don't believe that is true. I am very sure that mitigation is additive, not multiplicative. So four common shields give 40% mitigation. 4 rare 80%, and 4 very rare 120%. However, mitigation is capped a a certain level. Somewhere around 95% is the rumor. –  Jacob Eggers Jun 19 '13 at 0:49
@JacobEggers the rumor has been confirmed by NianticOpsBernini. –  Baarn Jun 26 '13 at 15:34
Well, NianticOpsBernini confirmed the 95% cap, but noted that the exact formula is confidential: groups.google.com/forum/m/#!msg/ingress-discuss/85ZfOoIsvnU/… –  nealmcb Jul 7 '13 at 18:42

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