|X reduced by y%||refers to an additive modifier|
|y% less||refers to a multiplicative modifier|
You have 1000 base damage and “10% reduced damage” from gear and “10% reduced damage” from passives. You can then choose between slotting either of two support gems:
|Gem A||10% reduced damage||gear+passive+gem = 30% reduced, so 1000*(1-0.3) = 700 damage|
|Gem B||10% less damage||(gear+passive)*gem = 20% reduced and 10% less, so 1000*(1-0.2)*(1-0.1) = 720 damage|
What this means in plain English is that you add the various “increased”/”reduced” effects together into a single multiplier, and multiply the base stat by the result, whereas you multiply the base stat by each “more”/”less” effect in turn.
The total stat value can be calculated as the sum of any added stat, multiplied by the sum of all increases and reductions to stat, multiplied by all more and less stat modifiers.
Stats are only applied once per calculation. The usual order of application is: