All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The best thing that a person could do for his deceased relative is to give charity on his behalf and intend the reward for him. 'Aa'ishah narrated that a man said to the Prophet said: "O, Prophet of Allaah, my mother died and did not leave a will. I think if she were able to speak, she would have given charity. Will she get any reward if I give charity on her behalf? The Prophet replied: "Yes, give charity on her behalf." [Al-Bukhari and Muslim] The scholars agreed in a consensus that the benefit of charity and supplication reach the dead. Imaam Muslim stated in his introduction of the authentic narrations reported by him that Ibn Al-Mubaarak said: "There is no difference of opinion about charity (that it reaches the dead)."
It is not a condition that the charity be given on the day a person died, indeed the reward reaches him regardless of the day when the charity was given. Believing that the reward of charity can only reach the dead if it was given on the day he passed away is wrong. As regards celebrating the anniversary of the death of a person, it is among the forbidden invented matters, and the best example is that of the Prophet .
Allaah knows best.