It is obligatory for a Muslim to make up any fasts missed during the month of Ramadan. These fasts should be made up before the next Ramadan arrives.

Shaykh Ibn Baz was asked about this matter and clarified the ruling. He stated that if a person delays making up the missed fasts until after the next Ramadan has begun, their situation must be examined. If the delay was due to a valid Islamic excuse, such as a continuous illness or a woman being pregnant or breastfeeding and unable to fast, then they are only required to make up the missed days. There is no expiation (kaffarah) required, even if it is delayed for several years.

However, if the delay was due to negligence and without a valid excuse, then according to the Shaykh, in addition to making up the fasts, the person must also pay an expiation for each day they delayed. This is the fatwa of a number of the Companions of the Prophet (peace be upon him).

The expiation consists of feeding one poor person for each missed day. The amount to be given is half a sa' of the local staple food, such as rice, dates, or wheat, which is approximately equivalent to 1.5 kilograms. For example, if someone missed five days and delayed making them up without an excuse, they must fast for five days and also feed five poor people.

If a person is poor and unable to feed others, then making up the fasts is sufficient, and the expiation is waived due to their inability to pay it.