Buff before fight start (barriers, iruka no Y, edo hiruzen, ...), when on field (anbu, ninjutsu urge, narutogirly, ...) and chakra/hp buff (kakuzu/asuma) are additive.

(X+Y+Z+...= buff%)

Scales (kushina, minato's chase, iruka Y, ...) and shreds (edo minato, 8t bee, gamakiri) are multiplicative.

(A*x% = B then B*x% = C then C*x% = D ...)