Allah describes those who "neglected the prayer and followed desires" and then says, "except one who repents, believes, and does righteous deeds" (Quran 19:59-60) — He mentions repentance and righteous action, not a count of make-ups. The four madhhabs, reasoning from the hadith "whoever forgets a prayer or sleeps through it, its expiation is to pray it when he remembers it" (Sahih al-Bukhari 597; Sahih Muslim 684), hold that missed prayers are made up. Ibn Hazm, Ibn Taymiyyah, Ibn al-Qayyim, and among later scholars Ibn 'Uthaymin, held that a prayer deliberately abandoned until its time expired cannot be validly made up at all, since its time was part of the act of worship; on this view the one who repents should be firm on the five daily prayers from now on and increase voluntary prayers, which Allah may accept in place of what was lost. Whichever position you follow, the practical advice is the same: guard today's prayers first, make up what you reasonably can alongside them, and never let an uncountable backlog become the excuse that keeps you from praying now.
Q&A · Repentance & Sin
I abandoned the prayer for years and now I've repented — do I have to make up every missed prayer?
Evidence — the daleel
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.