Excerpt from My Jewish Learning:
Traditionally, Jews are required to say the Kaddish for 30 days after burial for a child, spouse or sibling, and for 11 months after burial for a parent. From then on, one recites Kaddish (1) on a loved one’s yahrzeit (the Hebrew anniversary of their death) and (2) at Yizkor (memorial) services.
Some people say Kaddish for the departed not only at (1) and (2)
but daily at every prayer service. What is your opinion on this practice?