I am a woman in my forties and am married with children. I observe the prayer and other acts of worship, praise to Allah. I used to suffer from a chronic headache 24 years ago; that was before I got married. That was migraine. This caused me to break my fast each Ramadan for a few days, in addition to the days of my menstrual period. I have failed to make up for the days that I missed back then. Those days are too many to remember their number.
Shortly after marriage, I recovered. I wanted to make up for the days of fasting that I had missed. However, I could not remember exactly how many they were given that I had missed too many days. Shall I fast an infinite number of days? Or shall I do voluntary fasts and ask Allah for forgiveness? Or shall I fast and give charities with no count? Please advise me; may Allah reward you! I am now in my forties. I have done fasts and given charities with the intention of making up and expiating for the days of fasting that I had missed. However, I am not quite sure if I fulfilled what I have to do. Please advise me on what to do?

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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

First of all, you must know that there is nothing wrong with your breaking the fast since you were sick. Sickness allows fast-breaking. What you are required to do right away is to make up for the days of fasting that you have missed because of your sickness, in addition to the days that you have missed during your menses if you have not already done this. Allah, the Exalted, says: {…and whoever is ill or on a journey – then an equal number of other days...} [Quran 2: 185]

With this in mind, you should know that charities and other voluntary acts of worship are not sufficient to make up for the days of fasting that you have missed. You must fast what Allah has commanded you to fast. If you are not able to determine how many days of fasting you have missed, then do serious calculations and fast a number of days with which you mostly assure clearance of this obligation. This is all what you can do. Allah, the Exalted, says (what means): {So fear Allah as much as you are able.} [Quran 64: 16]

If you were able to make up for the days that you had missed at some point of time in the past but you did not do so and you did not have any excuse for not making up for them until another Ramadan came over, then you would have to offer an expiation in addition to fasting the days that you missed. The expiation is to feed a poor person per day of fasting that you delayed from its due time, as stated by the Companions of the Prophet, sallallaahu ‘alayhi wa sallam. 

If you have already fasted some of the days that you missed, then try to remember how many days you have made up for so far. If you are mostly sure that you have done all the fasts that you missed, then it is alright, and there is nothing more on you to do. If you are not sure, then you may continue to fast more days so as to make sure that your liability is totally cleared. Ibn Baz says, “The Muslim should hasten to make up for the missed fasts that he is most probably sure he has missed. Allah does not burden a soul with that which goes beyond its capacity.”

With this in mind, you need to fast the days that you are mostly sure you have missed. If you believe you have missed ten days, then observe ten days. If you believe you have missed more or less than ten days, then observe accordingly. Allah, the Exalted, says (what means): {Allah does not charge a soul except [with that within] its capacity...} [Quran 2: 286] Allah also says (what means):{So fear Allah as much as you are able.} [Quran 64: 16] You do not have to give charities; you are only required to make up for the missed fasts, unless you delayed a missed fast for no excuse until another Ramadan came over, as explained above.

Allah knows best.