What should one do if they have an unfulfilled fast or an unatoned fast, and it is difficult for them to calculate what they owe, whether it be expiation or making up missed fasts, due to various reasons such as not knowing the number, or being unable to fulfill an estimation, or fearing death before making up the fasts, or repeated invalidation of fasts?

Expiation (kaffarah (definition)) is only obligatory for breaking the fast by engaging in sexual intercourse during Ramadan (definition). As for breaking the fast by other means, such as masturbation, it only obligates making up the missed day (qada') without expiation.

Breaking a supererogatory (nafl) fast does not necessitate expiation. Scholars differ on whether it must be made up or not, and the most correct opinion is that it is not obligatory to make it up, but rather it is recommended.

Whoever is obligated to make up missed days or expiations and is unaware of their exact number must make up what brings certainty or strong probability that their obligation has been fulfilled. Whoever dies while making up missed days or fulfilling expiations after repentance, and was not negligent, is absolved of their obligation. Their heirs should feed on their behalf from their estate if it exists, or they may fast on their behalf.

The expiation for sexual intercourse during Ramadan is to free a slave. If one is unable, then to fast for two consecutive months. If unable, then to feed sixty poor people. If one is unable to feed, scholars differ on whether the expiation is waived for them or remains an obligation upon them.