I have many qadha namaz to make up but I'm not sure exactly how many because I did not keep count. how many should I do?

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You have to make up that which you are certain you missed. So let’s say you are not sure whether you missed 5 years of prayer, 6 years or 7 years. You are certain that you missed 5 years, but you don’t know if you missed more. In this case you are obligated to make up 5 years