It is obligatory upon you to make up for the days that you have failed to fast from this year and past years. If you did not know the number of days that you deliberately missed, you can consider it to be the lowest number of days that you are sure of. You should make up for the days that you have missed this last Ramadan before the next Ramadan. You do not have to make up for the rest of the days from previous Ramadans before the next Ramadan; however, you should not delay making up for them in such a way you are considered to be ignoring and negligent of the religious obligation. It is also obligatory to undertake the Kaffara for the deliberately missed fasts, and to pay the Fidya of 27 kg of food for every missed month, as explained in more detail in the treatise of Islamic laws.
