What is the ruling on counting good deeds, such as calculating the number of letters in the Qur'an and the reward that results from it, or displaying a good deeds counter while reciting the Qur'an?

Summary:

Whoever recites a letter from the Book of Allah receives a good deed, and a good deed is multiplied tenfold. Scholars have differed on what is meant by "letter" – whether it refers to a structural letter (like "alif") or a meaningful letter (like "alif lam mim," which consists of two meaningful letters). The opinion that it refers to a structural letter multiplies the reward.

Counting the letters of the Quran is permissible, and some of the Salaf did so. There is no harm in saying that reading the entire Quran may lead to immense reward, equivalent to the number of letters multiplied by ten good deeds.

Counting good deeds or using a counter for them was disliked by some of the Salaf, and it is feared that it may lead to arrogance and self-admiration. Abdullah ibn Mas'ud disliked counting and reminded that acceptance is in the hand of Allah, and that the believer should be between hope and fear, and not be deluded by their deeds.