How do +Dodge skills and passives stack in Diablo 3?

Solution 1:

Dodge percentages multiply out. First, start by thinking of x% dodge as (100-x)% chance to be hit. Specifically, 15% dodge = 85% chance to be hit.

75% base => 25% dodge
75% base * 85% from passive = 63.75% chance to be hit => 36.25% chance to dodge
75% base * 85% from passive * 85% from mantra = 54.1875% chance to be hit => 45.8125% chance to dodge

... and so on. The dex->dodge conversion is also non-linear, but it's not the usual x / (y + x) formula.

Solution 2:

Catalept answered already while I was typing this; so I'm leaving out the detailed explanation, but posting as it explains your actual scenario.

The calculation is multiplicative; so

• Base dodge: 0.25
• Guardian's Path (15%): 0.15
• Mantra of Evasion: 0.15
• Evasion first 3 secs: 0.15

would result in

(1 - 0.25)(1 - 0.15)(1 - 0.15)(1 - 0.15) = 0.75 * 0.85 * 0.85 * 0.85 = 0.46059375 ~= 0.461

So you have 46.1% chance to be hit; ie. 53.9% dodge