When it is possible to pay the khums to whoever deserves it or to the agent, one should hasten to do so. One can use the rest of the money whether he paid the khums or not.

If one pays khums every week from his weekly salary, then he does not have to pay khums at end of the khums year. If he did not do so, as he is permitted to delay the payment of khums until the end of the khums year, then he can pay the khums from the remainder of his earnings after the payment of the yearly expenses.

Khums is obligatory once a year. It is on what exceeds the expenses during the year. One should refer to an agent of the marji', and determine a fixed yearly time to pay khums after calculating it.

It is obligatory on every duty-bound individual to determine a khums fiscal year and calculate the remaining money after covering his expenses and pay the fifth of the remainder.

With the assumption that you paid khums on the capital money before you used it for the business, at the end of the khums year the debts and all other paid expenses for that year are deducted from the profits, and khums is due on the remaining balance. If the balance is zero or negative, no khums is due for that year.

His pilgrimage is valid. He must hasten to pay Khums.

If you work in a state establishment and your salary is transferred directly to a state-owned bank, then the laws of khums and Hajj do not apply on the salary. They both apply on amounts that you withdraw from the bank. Both conditions must be present (working for the state and the bank being owned by the state) in order for this ruling to apply.
If one of the two conditions are not fulfilled, like if you work for a private establishment or the amount is transferred to a private bank, or both of them are not present, the regular laws of Khums and Hajj apply. That is, if the amount adds up to what is sufficient to cover the cost of Hajj, it becomes obligatory. Likewise, Khums has to be paid from the unused portion of it at the end of the Khums year.

If denying the obligation of khums means a denial of its obligation on the unused amount of the yearly income, then this does not affect the person being regarded as a Muslim. However, denying the khums in an absolute way is a clear rejection to the Quranic verses and the traditions of the Prophet (peace be upon him and his holy progeny).

Khums is not obligatory on expenses if they were spent in prohibited ways. However, a believer is expected not to perform any prohibited thing even if he thinks it is small, since it is a disobedience to Almighty Allah.

Yes, it is permissible to do so. The religious responsibility of paying the khums is on the owner of the money and it is not on the person that makes use of it or benefits from it.

It is not permissible to pay such financial obligations to the consumer of wine and it is permissible to do so to sinners if they are needy. Based on compulsory precaution, it is not permissible to pay the committer of major sins which are worse than consuming wine, such as not performing the prayers.

May Allah accept from you this sincere intention in upholding His teachings and obligations.
Khums is a divinely-prescribed obligation. It is the fifth of the yearly income after deducting expenses. It can be calculated as a fifth of all the monies that is in one’s possession plus the fifth of the worth of the items that were unused during the year.
This khums amount is divided into two equal amounts:
The first one is the share of Sayyids. It should be spent on needy people from the clan of Hashim, the great-grandfather of the Prophet (peace be upon him and his progeny).
The second one is the share of the Imam (peace be upon him). It should be given to the religious Adil Marji who is able to spend it in accordance to what pleases the twelfth Imam (peace be upon him).

One should refer to the Marji or his agents for that.

Khums is a divinely-ordained financial obligation. It is the fifth of the yearly income that remains unspent. So, you should determine a specific day to calculate your profits in coordination with the Marja’ or his appointed agent. Every year on this specific day, you calculate the fifth of all the net income that you possess plus the fifth of the worth of items that were not used during the year.
The khums amount is divided into two equal amounts: one is to be given to needy people amongst the offspring of Hashim – the great-grandfather of the Prophet (peace be upon him) – and the second is to be spent with the coordination of the Marja’ by referring to him or his appointed agent to spend it in the ways of serving the religion and fulfilling the necessities of the believers.

Your net wealth is $1000, whereas $800 is the 80% of last year’s net income after khums was paid. This means that your net income for this year is $200 from which you have to pay khums ($40). Therefore, for the next year $960 will be exempted from khums ($800 from the previous year, plus $160 remaining from the current year).

If the salary payments are deposited in an account in a private or government bank, then it is subject to khums. This also applies to a transfer of the salary payments to an account in a private bank.
If the salary payments are transferred into an account in a government bank, then it not considered owned until it is withdrawn physically and khums is not due before that.
It is obligatory to pay khums at the end of the khums year from what remains after any expenses paid.

Khums is not obligatory on the loan, it is obligatory on the profits.

It is not obligatory to pay Khums from monies that Khums was paid from in past years.

If they were used, then it is not obligatory to pay khums for them. Otherwise, they are subject to khums once.

If what you need can only be obtained in a larger quantity, then khums is not applicable on what remains from that. For example, if you need a notebook of 20 pages, but you could not find a 20-page notebook, and the closest to it is a 100-page notebook, then the unused part of the notebook will not be subject to khums. Similarly, if you need 20 pens, and you can purchase 20 pens without needing to buy 100 pens, then the unused pens will be subject to khums.