Guild Wars 2

I would like to know if bonus damage multipliers stack additive or multiplicative.

I am not aware of any post that concern this and guildwars 2 wiki do not have any information on that either.

For example: if you have the guardian trait: [Powerful Blades], it grants increase in sword damage by 10%. If you have Superior Sigil of Force, it grants another 5%. If you have Superior Rune of Strength (6), it grants another +7% under might. If you have [Power of the Virtuous], it grants another on average +3% for 3 boons.

The question is would the total be: 10% + 5% + 7% + 3% = 25% increase (additive), in which case the bonus damage multiplier would be 1.25?

Or would it be the case 1.1 × 1.05 × 1.07 x 1.03 = 1.272925 which would be effectively a 27% damage increase?

As far as I know it’s additive, for example if you get the traits that adds +10% and +5% damage you will obtain an increase of 15% in damage.

edit: nvm looking at some other threads it seems to be multiplicative
https://forum-en.gw2archive.eu/forum/professions/guardian/Damage-modifiers-vs-power/first#post2524806

It has been shown conclusively that the multipliers work multiplicatively. If you want to re-check it, go to the heart of the mists, get a steady weapon and play with the golems.

A guardian with scepter and with/without the scepter 10% trait and Unscathed Contender should be optimal for your purpose.

Its multiplicative. 10% + 5% + 7% + 3% = ~27.3%