A Margin Loan can be utilised to purchase just one stock. However, before considering in investing in just one stock, you will need to consider how much you wish to borrow. In the case of the top 20 shares listed on the ASX, we lend up to 65% of the current value of these shares, of course, the scenario can change if more than one stock is purchased. 
The example below illustrates the different scenarios regarding Lending Values:

A 65% lending value is allocated on a single share, this increases to 70% if you hold 2 to 4 shares and 75% if 5 or more approved shares are held in your portfolio. This example generally applies to the top 20 shares and lending values will vary according to the shares being considered, and are subject to change. A full list of shares that CommSec Margin Lending lends against can be found on the CommSec website, commsec.com.au.
How to get started: If you are looking to purchase $10,000 of a stock which has a lending value of 65%, you will need to provide us with 35% of the value upfront or $3,500 in cash. Alternatively, if you already hold shares, and they are listed on our approved shares list, you will be able to utilise these shares to borrow funds on a margin loan. Of course, depending on what shares you currently hold will determine how much you can borrow. 
By holding a diversified portfolio with CommSec, you will also gain access to ‘bonus stocks’ listed on the CommSec approved shares list, comprising of mid to small companies, whereby an LVR is applicable for diversified Portfolio’s only. So, if you want to invest in these mid to small companies, having 5 or more approved shares will allow you to borrow against them. Having a single share exposure increases the likelihood of a margin call, for example, if a company reports a downgrade in their annual profits, this may have an impact on the share price, and could cause a margin call if the fall is substantial. Having a well diversified portfolio will lessen the impact because you have spread your risk across different shares. In addition to this, having exposure to different market sectors will also allow you to weather an unfavourable fall in a particular market sector.  We encourage investors to seek independent financial advice before considering any gearing product. If you have any questions please feel free to visit commsec.com.au or call us on 13 17 09, Monday to Friday, from 8 AM to 8PM (EST). By Stephen Karpin, General Manager, CommSec 
Important InformationThe views expressed in this article are those of Stephen Karpin, a representative of Commonwealth Securities Limited (CommSec) ABN 60 067 254 399 AFSL 238814.  CommSec is a wholly owned but non-guaranteed subsidiary of the Commonwealth Bank of Australia ABN 48 123 123 124 AFSL 23495 (the Bank) and a Participant of the ASX Group. As this information has been prepared without considering your objectives, financial and taxation situation or needs, you should, before acting on this information, consider its appropriateness to your circumstances and if necessary, seek appropriate professional financial and taxation advice.  CommSec Margin Loan is a facility provided by the Bank and is administered by CommSec. Please be aware that a CommSec Margin Loan exposes you to unfavourable movements in the value of shares and units in managed funds, and possibly to margin calls. Please be aware that you are personally liable for any shortfall that occurs should your entire portfolio have to be sold to answer a margin call where there have been falls in the market value of your investments. Only investors who fully understand the risks associated with gearing into investments should apply. All applications are subject to the Bank’s credit approval process. Fees and charges apply.  Please consider the Product Disclosure Statement, and terms and conditions, issued by the Bank and available from www.commsec.com.au before making any decisions.