Is it permissible to pay the expiatory fast (kaffarat al-siyam) at any time, even if I am not fasting, after completing the making up of a previous fast?

It is preferable for the feeding to coincide with or follow the making up of the fast, but this is not a condition. It is permissible to give the expiation before, after, or during the making up of the fast, whether the person is fasting or not. The expiation for delay (kaffarat al-ta'kheer) is obligatory for whoever delays making up for Ramadan without a valid excuse until the next Ramadan begins. This consists of feeding one poor person for each day a mudd of food (approximately 750 grams of rice).