Is there a way to give charity on behalf of my deceased father's missed prayers, and how can the number of missed prayers and the amount of charity for them be calculated?

Scholars have concluded that one who abandons prayer out of negligence and laziness is a disbeliever, based on the Prophet's (peace be upon him) saying: "The covenant between us and them is prayer; whoever abandons it has disbelieved," and his saying: "Between a man and disbelief and polytheism is the abandonment of prayer."

Accordingly, it is not permissible to give charity on behalf of one who abandons prayer, nor to fast or perform Hajj on their behalf, nor to seek forgiveness for them, nor to attend their funeral, nor to bury them in Muslim cemeteries.

However, if your father was ignorant of the obligation of prayer, or if he followed those who ruled against the disbelief of one who abandons prayer out of negligence, then we hope that Allah will forgive him and that supplication, seeking forgiveness for him, and giving charity on his behalf will benefit him.