Answered by Shaykh Yusuf Weltch
I have about 17 years’ worth of missed prayers. But in that 17 years, I was praying on and off. So I did not forget all of it entirely. How should I calculate how many prayers to make up? And what happens to those extra prayers if the amount estimated and made up is more than what I missed?
In the Name of Allah, the Most Merciful and Compassionate
Please see the below-given link for information on calculating missed prayers.
Estimating the Number of Makeup Prayers
If, in the end, you made up more prayers than were necessary, those extra prayers will be taken into account as extra voluntary prayers, and you will receive their reward on the Day of Judgment. [Maydani, al-Lubab fi Sharh al-Kitab]
This is why it is safer and more cautious to pray more prayers than to pray less. As you will see in the answer linked above, you should add to your final calculation for the sake of caution.
Hope this helps
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani
Shaykh Yusuf Weltch is a teacher of Arabic, Islamic law, and spirituality. After accepting Islam in 2008, he then completed four years at the Darul Uloom seminary in New York where he studied Arabic and the traditional sciences. He then traveled to Tarim, Yemen, where he stayed for three years studying in Dar Al-Mustafa under some of the greatest scholars of our time, including Habib Umar Bin Hafiz, Habib Kadhim al-Saqqaf, and Shaykh Umar al-Khatib. In Tarim, Shaykh Yusuf completed the memorization of the Qur’an and studied beliefs, legal methodology, hadith methodology, Qur’anic exegesis, Islamic history, and a number of texts on spirituality. He joined the SeekersGuidance faculty in the summer of 2019.