How to calculate how far a stock price can drop before a broker would issue a margin call?
With your numbers, look at it this way - You borrowed $50. When the stock is $100, you are at 50% margin.  What's most important, is that there's margin interest charged, so the amount owed will increase regardless of the stock price. When calculating your return or loss, the interest has to be accounted for or your numbers will be wrong. For a small investor, margin rates can run high, and often, will offset much of your potential gain. What good is a $100 gain if you paid $125 in margin interest?
"First, you are not exactly ""giving"" the brokerage $2000. That money is the margin requirement to protect them in the case the stock price rises. If you short 200 shares as in your example and they are holding $6000 from you then they are protected in the event of the stock price increasing to $30/share. Sometime before it gets there the brokerage will require you to deposit more money or they will cover your position by repurchasing the shares for your account. The way you make money on the short sale is if the stock price declines. It is a buy low sell high idea but in reverse. If you believe that prices are going to drop then you could sell now when it is high and buy back later when it is lower. In your example, you are selling 200 shares at $20 and later, buying those at $19. Thus, your profit is $200, not counting any interest or fees you have paid. It's a bit confusing because you are selling something you'll buy in the future. Selling short is usually considered quite risky as your gain is limited to the amount that you sold at initially (if I sell at $20/share the most I can make is if the stock declines to $0).  Your potential to lose is unlimited in theory. There is no limit to how high the stock could go in theory so I could end up buying it back at an infinitely high price. Neither of these extremes are likely but they do show the limits of your potential gain and loss.  I used $20/share for simplicity assuming you are shorting with a market order vs a limit order. If you are shorting it would be better for you to sell at 20 instead of 19 anyway. If someone says I would like to give you $20 for that item you are selling you aren't likely to tell them ""no, I'd really only like $19 for it""" Yes, it can buy back the call, but much before stock hits the $30 mark.   Let us say you got 1$ from selling the call. So the total money in your account is 4$ + 1 $ = 5 $. When stock hits 10$ (your strike), the maintenance margin is 5$. As soon as stock goes past 10, your maintenance margin is violated. So broker will buy back your call (at least IB does that, it does not wait for a margin call). Now if the stock gapped up from 8 to 30,then yes, broker will buy it back at 30, so your account will have a negative balance. Assume the call cost 20$ when stock hit 30, your balance is: 5 - (30-10) = -15. Depending on broker, I suppose they will ask you to bring your account balance back up to positive. If they don't do that, they risk going out of business. how do they turn shares into cash that they can then use to grow their business? Once a Company issues an IPO or Follow-On Public Offer, the company gets the Money. Going over the list of question tagged IPO would help you with basics. Specifically the below questions; How does a company get money by going public in an IPO? Why would a company care about the price of its own shares in the stock market? Why would a stock opening price differ from the offering price?  From what I've read so far, it seems that pre-IPO an investment bank essentially buys the companies public shares, and that bank then sells them on the open market. Is the investment bank buying 100% of the newly issued public shares? And then depositing the cash equivalent into the companies bank account? Additionally, as the stock price rises and falls over the lifetime of the company how does that actually impact the companies bank balance? Quite a bit on above is incorrect. Please read the answers to the question tagged IPO. Once an IPO is over, the company does not gain anything directly from the change in shareprice. There is indirect gain / loss. A CFD broker will let you open a trade on margin as long as your account balance is more than the margin required on all your open trades. If the required margin increases within a certain percentage of your account balance, you will get a margin call. If you then don't deposit more funds or close losing trades out, the broker will close all your trades. Note: Your account balance is the remaining funds you have left to open new trades with. I always use stop loss orders with all my open trades, and because of this my broker reduces the amount of margin required on each trade. This allows me to have more open trades at the one time without increasing my funds. Effects of a Losing Trade on Margin Say I have an account balance of $2,000 and open a long trade in a share CFD of 1,000 CFDs with a share price of $10 and margin of 10%. The face value of the shares would be $10,000, but my initial margin would be $1,000 (10% of $10,000).  If I don't place a stop loss and the price falls to $9, I would have lost $1,000 and my remaining margin would now be $900 (10% of $9,000). So I would have $100 balance remaining in my account. I would probably receive a margin call to deposit more funds in or close out my trade. If I don't respond the broker will close out my position before my balance gets to $0. If instead I placed a stop loss at say $9.50, my initial margin might be reduced to $500. As the price drops to $9.60 I would have lost $400 and my remaining margin would now only be $100, with my account balance at $1,500. When the price drops to $9.50 I will get stopped out, my trade will be closed and I would have lost $500, with my account balance still at $1,500. Effects of a Winning Trade on Margin Say I have the same account balance as before and open the same trade but this time the price moves up. If I don't place a stop loss and the price goes up to $11, I would have made a $1,000 profit and my remaining margin will now be $1,100 (10% of $11,000). So my account balance would now be $2,000 + $1,000 - $1,100 = $1,900. If I had placed a stop loss at say $9.50 again and the price moves up to $10.50, I would have made a profit of $500 and my margin would now be $1,000. My account balance would be $2,000 + $500 - $1,000 = $1,500. However, if after the price went up to $10.50 I also moved my stop loss up to $10, then I would have $500 profit and only $500 margin. So my balance in this case would be $2,000 + $500 - $500 = $2,000. So by using stop losses as part of your risk management you can reduce the margin used from your balance which will allow you to open more trades without any extra funds deposited into your account. "If your shares get called on stock at a price below what you paid for the stock, your gain or loss depends on what premium you got for the options you sold.  ""can I deliver shares at that assigned strike using margin or additional capital if I have it? Can the broker just take care of it and let me collect the time premium? "" You don't need margin or any cash because you already hold the shares. A covered call means your cash requirements are 'covered'. So they'll just buy your shares at the strike price of $50. And you still get to keep the premium (which you should have gotten when you sold the covered call).  You only need cash or margin when you've sold an uncovered call or put." Generally speaking.  1. Take the position size / average daily volume.  2. Multiply that number by 10 or whatever 1/whatever % of volume you think you can execute, ( you can at best acct for 10 percent of traded volume on a day).  3. You now have days until liquidation (x)  4. Take the days until liquidation sample the return over  time x. I.e. if days until liquidation is 10, you would sample 10 day returns.  5. Calculate the distribution characteristics of this window (mean, var, skew, kurt) and calculate VaR based on some confidence.  You can now have a liquidity risk expected loss and a VaR.  If position is on margin don't forget to add the interest cost.  Note: Instead of taking 10 day return, you can take the 10 day VWAP and calculate return between Open and 10 day vwap. It is a question of how volatile the stock is perceived to be, its beta correlation to the S&P500 or other index. Margin requirements are derived from the Federal Reserve, Self Regulatory Organizations, the exchange itself, the broker you use, and which margining system you are using. So that makes this a loaded question. There are at least three margin systems, before you have your own risk officer in a glass room that doesn't care how leveraged up you get. Brokers primarily don't want to lose money. Ok, so disregarding passivity, could you help me through a simplified example?   Say I only had two assets, SPY and TLT, with a respective weight of 35 and 65% and I want want to leverage this to 4x.  Additionally, say daily return covar is:  * B/B .004% * B/S -.004% * S/S .02%   Now, if I read correctly, I should buy ATM calls xxx days in the future.  Which may look like: Ticker, S, K, Option Price, Delta, Lambda  * TLT  $126.04  $126.00  $4.35  0.50  14.5 * SPY  $134.91  $134.00  $6.26  0.55  11.8  ^ This example is pretty close but some assets are far off.   I feel like I'm on the wrong track so I'll stop here.    I just want to lever up my risk-parity. Margin rates are too high and I'm docked by Reg-T.