We establish formulas for computation of the higher algebraic K-groups of the endomorphism rings of objects linked by a morphism in an additive category. Let C be an additive category, and let Y → X be a covariant morphism of objects inEnd C ,Y (X) is the quotient ring of the endomorphism ring End C (X) of X modulo the ideal generated by all those endomorphisms of X which factorize through Y . Moreover, let R be a ring with identity, and let e be an idempotent element in R. If J := ReR is homological and R J has a finite projective resolution by finitely generated projective R-modules, then K n (R) ≃ K n (R/J) ⊕ K n (eRe) for all n ∈ N. This reduces calculations of the higher algebraic K-groups of R to those of the quotient ring R/J and the corner ring eRe, and can be applied to a large variety of rings: Standardly stratified rings, hereditary orders, affine cellular algebras and extended affine Hecke algebras of typeÃ.