When should I make up the missed fasts?

The majority of scholars, including the Hanbali, Maliki and Shafi'i schools, hold the view that missed fasts from Ramadan should be made up before the arrival of the next Ramadan, unless there is a valid excuse preventing a person from doing so (explained in the next question).

Their evidence is based on the Hadith of Aishah (Radiyallahu 'anha), who said: “I had to make up some of my Ramadan fasts, but I was unable to do so until Shaaban, due to being occupied with the service of the Messenger of Allah (peace and blessings be upon him).” (Reported by al-Bukhari and Muslim). This Hadith shows that Aishah (Radiyallahu 'anha), knew that she needs to make up her missed fasts before the next Ramadan arrived.

The Hanafis differed on this point. They consider that making up missed Ramadan fasts is obligatory, but without a strict deadline. In their view, it is not sinful to delay making up the fasts beyond the next Ramadan, whether or not a person has a valid excuse. However, they still emphasize that it is better and preferred to make up the fasts as soon as possible. The Hanafi school position is based mainly on the Quranic verse: “So whoever sights [the new moon of] the month, let him fast it; and whoever is ill or on a journey - then an equal number of other days. (Surah al-Baqarah, 2:185). Since the verse does not specify a time limit, they understood that the obligation is without restriction to a particular timeframe.