Khums literally means “one-fifth or 20%”. In Islamic legal terminology, it means “one-fifth of certain items which a person earns by means of trade, industry, agricultural work, research or any other ways of earning, like, if he earns some money by working in a government department, and if it exceeds the annual expenses for maintaining himself and his family, he should pay Khums (i.e. 1/5) from the surplus, in accordance with the rules.
Khums is one of the mandatory rites of the religion of Islam and it is an essential obligation like Jihad. The importance given by the Quran to the issue of Khums can be understood from the following verse: "And know that out of all the booty that ye may acquire (in war), a fifth share is assigned to Allah, - and to the Messenger, and to near relatives, orphans, the needy, and the wayfarer, - if ye do believe in Allah and in the revelation We sent down …"
It should be noted that the rules regarding certain important obligations like fasting and Hajj have been given in very few verses of the Holy Quran. There are not more than three or four verses about them in the Quran. Likewise the Quran has not made mention of the obligatory parts or segments of such obligations, their basic elements, conditions etc. that are important. All those details have been relegated to the Prophet (pbuh) and his righteous successors.
The grand religious authorities (jurisprudents) relying on Quranic verses as well as traditions have said that Khums is obligatory on the following seven things:
- Profit or gain from earning.
- Treasure trove.
- Amalgamation of Halal wealth with Haraam.
- Gems obtained from the sea diving.
- Spoils of war.
- As commonly held, a land which a zimmi (a non-Muslim living under the protection of Islamic Government) purchases from a Muslim.
However, what is frequently asked about and is an issue faced by most Muslims across the world concerns the first part i.e. “profit or gain from earning” about which the jurisprudents say:
“If a person earns by means of trade, industry or any other ways of earning, like, if he earns some money by offering prayers and fasting on behalf of a dead person, and if it exceeds the annual expenses for maintaining himself and his family, he should pay Khums from the surplus in accordance with the rules.” For further information in this regard, you can refer to index: 690 (Payment of Khums and Permission of Maraje’) on our website.
For instance, if an employee receives his first salary at the end of January and spends all his annual income in a regular manner for maintaining himself and his family until the end of the month of January of the next year, Khums is not payable on his income. In case his income exceeds the annual expenses for maintaining himself and his family at the end of January next year (though he may economized and been frugal or for example he has deposited it in his bank account), he should pay 1/5th of it to the office of the Marja (qualified Mujtahid) whom he follows so that he (Marja) will have to spend it for such purposes as deemed appropriate by him.
 Chap. Al-Anfal: 41 وَ اعْلَمُوا أَنَّما غَنِمْتُمْ مِنْ شَیْءٍ فَأَنَّ لِلَّهِ خُمُسَهُ وَ لِلرَّسُولِ وَ لِذِی الْقُرْبى وَ الْیَتامى وَ الْمَساکینِ وَ ابْنِ السَّبیلِ إِنْ کُنْتُمْ آمَنْتُمْ بِاللَّهِ وَ ..؛ Extracted from index: 898.
 Tawzih al-Masail (with annotation by Imam Khomeini) vol.2, p. 7, issue No. 1751.
 Ibid, issue No. 1752.