The fast observed during the month of Ramadan (Month of Fasting) are Fard (Compulsory) fasts. Every sane Muslim adolescent and adult must fast through the month of Ramadan (Month of Fasting). Ignoring or missing any of them without a valid reason is a great sin. Travelers, sick people, women during menses or after childbirth are required to postpone their fasts. Missed fasts have to be compensated by fasting at a later date. Terminally ill patients or really weak people who cannot go through the rigors of fasting have to feed a poor person for each missed fast.

Besides the 29 or 30 Fard (Compulsory) Fasts of the month of Ramadan (Month of Fasting), there are Nafl (Extra Obligatory) fasts also. Any act of worship followed and demonstrated by the last Messenger of Allah, Muhammad صلى الله عليه وسلم besides Fard is a Nafl.

All Nafl (Extra Obligatory) 'Ibadah (Acts of Worship) are from Sunnah (Traditions of Muhammad صلى الله عليه وسلم).

Kinds of Fasts

1. Fard (Compulsory) Fasts
2. Nafl (Extra Obligatory) Fasts
3. Haram (Unlawful) Fasts.

1. Fard (Compulsory) Fasts:

Only the fasts of Ramadan (Month of Fasting) are Fard (Compulsory) Fasts. If they are missed without any genuine reason, there is a special penally for a missed fast. And if these fasts are missed due to a genuine reason like sickness or travel, it is also obligatory to observe the Qada (Make-up) of these fasts at some other time, but all missed Fasts must be compensatd in the same Islamic year.

2. Nafl (Extra Obligatory) Fasts:

These are extra obligatory fasts which the Messenger of Allah, Muhammad صلى الله عليه وسلم used to observe like the fast of 10th of Muharram, the fast of ‘Arafah i.e. on 9th of Dhul Hijjah and the fasts of Ayyamul Bid i.e. 13th, 14th, and 15th of every lunar month. To be Nafl means that it is not necessary to observe them, but it is always good to observe them. There are six fasts in the month of Shawwal after 'Id al-Fitr, fast on the 15th of Sha’ban etc.
(In the year 11 Hijrah, the Messenger of Allah, Muhammad صلى الله عليه وسلم decided to observe Nafl Fasts on two consecutive days i.e. 9th and 10th or 10th and 11th of Muharram, to differentiate from the Jewish traditions; but unfortunately he did not see the Muharram of 12 Hijrah. Muslims must observe two consecutive fasts in Muharram as a (Tradition of Muhammad صلى الله عليه وسلم).

3. Haram (Unlawful) Fasts:

Only five fasts are Haram during the year. They are the fasts on ‘Id al Fitr, ‘Id al Ad-ha and the fasts on Ayyamut Tashriq which are 11th, 12th and 13th of Dhul Hijjah.