What should I do and how can I repent after having wasted years of my life in forbidden amusement, abandoning prayer, and committing grave sins? Do I have to make up for 15 years of past prayers after repentance? How do I calculate the missed prayers, and is my calculation correct? Does martyrdom for the sake of Allah erase my past omissions of prayer, sins, transgressions, and grave misdeeds?

The one who repents from a sin is like one who has no sin. Exaggerating the path to salvation and fearing Satan might lead to distancing oneself from Allah.

Scholars differed on making up missed prayers due to laziness. The majority believe in the obligation of making them up, while Sheikh al-Islam Ibn Taymiyyah holds that it is not prescribed.

According to the majority opinion, it is sufficient to make up as many prayers as you are able, for Allah does not burden a soul beyond its capacity. And if you die before making up all that is due, Allah is Forgiving and Merciful.

Jihad in the way of Allah expiates all sins except debt. So, if you are killed as a martyr, your sins will be forgiven except for debt.

To calculate missed prayers: Estimate the number of years since puberty during which you did not pray, then calculate the obligatory prayers. If you don't reach a certain number, then strive in your estimation until you are reasonably sure that your liability is cleared.