Assalamualaykum. My question is regarding making up prayers. I made a note based on my memory. I reach my age of puberty since around 2013. Then in the same year until 2015, I can't remember how many fasts did I miss because of menses. My menses were not regular at that time (sometimes it happened once in a month but sometimes it doesn't) so I cannot remember whether I have missed fast or not and even if I have, I can't remember how many, the only thing that I remember is that I have 3 weeks of missed fast in one of the year (between 2013 until 2015) because of menses (I never knew about istihadah so I did not fast at that time). Can I assume that in the other two years (beside where I did not fast 3 weeks), I missed fast 7 days each? So, I have 35 fasts during those years?Secondly, in last year, I remembered making up fast for one day. According to my notes in that year, I only have 35 missed fasts (from the previous years) and I did not write more than that. So I assume that I only have one day missed fast during last year, which I have made up. But I feared of having more missed fast more than that, so what should I do? Can I just keep assuming that I have made up my fast during last year and continue making up missed fast from the previous years because of my ignorance? I have repented and want to make them up.My last question, do I have to make up those fasts (from previous years) before next ramadhan comes? I apologize for the long question and may Allah reward you.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

According to the view of the majority of the scholars, you must make up all the days you did not fast last Ramadan and which you did not make up; this must be done before the beginning of the following Ramadan.

If you do not know for certain the number of days that you have to make up, then you should estimate the number and make up enough days with which you become certain or predominantly think that you are acquitted from liability. This is the only thing that you can do, and Allah does not burden a soul more than it can bear.

Hence, if you predominantly think that you did not break the fast in the previous years except the days that you mentioned, and that last year you only broke the fast for one single day, then you should act according to this, and you will be acquitted from sin by doing so; Allah willing.

Moreover, if you knew that it is forbidden to delay making up for the missed days of Ramadan until the advent of the following Ramadan without a sound reason, then you have to repent to Allah for delaying making up for the missed days.

According to the view of the majority of the scholars, you also have to feed a poor person for each day that you delayed making up, a Mudd of food, which is approximately 750 grams.

However, if you were unaware of the prohibition of delaying making up for the missed days [until the next Ramadan came], then you are not required to do anything, but you have to hasten in making up for whatever days that you had missed, as we have already mentioned.

For more benefit, please refer to Fataawa 114245, 101245, 23630, 136499 and 90795.

Allah knows best.