What do you mean by/How do you calculate "Additively" and "Multiplicatively" in terms of Warframe mods?

[Lorienzo]

As above :/

Examples please?

[UltimateGrr]

Mods stack additively with each other, meaning if 2 mods add +HP, the final modifier would be the sum of those two mods (Vigor's +120% HP and Vitality's +440% would increase HP +560%).  Mods apply their modifies to the relevant base stat multiplicatively (Excalibur has 100 base HP, so a +560% bonus would give him +560 hp, or 660 before rank bonuses, while Nidus's base 150 HP would get 840 HP added on, for 940 HP before rank bonuses)

[Xzorn]

Mods in Warframe can be overly complicated in terms of their effects.

Some effects are additive with each other and others multiplicative. Sadly it's hard to say exactly from a stat because even when a mod says exactly the same thing it can act completely differently.

As example Condition Overload, Pressure Point and the Steel Charge Aura all say +%Melee Damage. Steel Charge and Pressure Point are additive with each other and affect your base weapon damage ie Pressure Point is +120% and Steel Charge is +60%, together they would give you +180% base weapon damage.

Condition Overload, even though it says +60% Melee Damage is actually multiplicative. Even more so, it's multiplicative with each stack. Instead of 120% + 60% +60%. You instead have (1 + 1.2 + 0.6) * 1.6,

Most mods are technically multiplicative to whichever stat they affect but the term is most often used to distinguish the difference from how the mod interact with other mods or buffs. It would be best to check the wiki for a mod if you're curious since about 90% of the time the information is correct on mod interactions.