We determine Grothendieck groups of periodic derived categories. In particular, we prove that the Grothendieck group of the m-periodic derived category of finitely generated modules over an Artin algebra is a free Z-module if m is even but an F2-vector space if m
Nearby in the stack
is odd. Its rank is equal to the number of isomorphism classes of simple modules in both cases. As an application, we prove that the number of non-isomorphic summands of a strict periodic tilting object
T
, which was introduced in [S21] as a periodic analogue of tilting objects, is independent of the choice of