When you open a brokerage account, you are typically given a choice between a "Cash Account" and a "Margin Account." Understanding the structural differences between these two is the first step in mastering the mechanics of borrowing to invest.

Cash Accounts: The Traditional Path

In a cash account, the rules are simple: you can only trade with the money you have physically deposited. If you have $1,000 in your account, you can buy $1,000 worth of stock. There is no borrowing, no interest, and no risk of losing more than your initial investment.

One major limitation of cash accounts is the "settlement" rule. When you sell a stock, it takes time for the money to officially move from the buyer to your account (usually one or two business days). In a cash account, you often have to wait for these funds to settle before you can use them to buy something else. Furthermore, day trading is restricted in cash accounts; you must pay for every security in full before you are allowed to sell it .

Margin Accounts: The Flexible Alternative

A margin account is essentially a line of credit attached to your investment portfolio. It allows you to bypass settlement delays and, more importantly, borrow funds to increase your position sizes.

The Minimum Margin Requirement

Before you can even think about borrowing, you must meet the "Minimum Margin" requirement. By law (FINRA Rule 4210), you must have at least $2,000 in equity (cash or eligible securities) to engage in margin trading . Some brokerage firms, known as "house" rules, may require even more—sometimes $5,000 or $10,000—depending on their internal risk assessment. If your account balance drops below this minimum, your ability to borrow is suspended until you deposit more funds.

Initial Margin: The 50% Rule

Once your account is active and meets the minimum requirements, you encounter "Initial Margin." This is the percentage of the purchase price that you must pay for with your own cash. Under Federal Reserve Board Regulation T (Reg T), the initial margin requirement for most stocks is 50% .

Example of Initial Margin:

You want to buy $10,000 worth of "Company X."
Reg T requires a 50% initial margin.
You must provide $5,000 of your own money.
The broker lends you the remaining $5,000.

It is important to note that you don't have to borrow the full 50%. You could choose to put up 70% and only borrow 30%. The 50% rule is simply the maximum limit allowed by law for most securities .

Maintenance Margin: The Safety Net

After you have purchased the stock, the rules change. You no longer look at the Initial Margin; you look at the "Maintenance Margin." This is the minimum amount of equity you must keep in your account as the stock price fluctuates.

FINRA rules state that your equity must not fall below 25% of the current market value of the securities in your account . However, many brokers set their "house" maintenance requirements higher, such as 30% or 40%, to give themselves a buffer .

Feature	Cash Account	Margin Account
Borrowing	Not allowed	Allowed up to 50% initially
Minimum Equity	$0 (or broker minimum)	$2,000 (FINRA requirement)
Interest Charges	None	Charged on borrowed balance
Short Selling	Not allowed	Allowed
Risk Level	Limited to deposit	Can exceed initial deposit
Settlement	Must wait for funds	Immediate use of funds

The Role of "House" Requirements

While federal and industry rules (Reg T and FINRA) provide the floor, individual brokerage firms have the authority to be stricter. A broker might decide that a particularly volatile stock—like a new tech IPO or a "meme" stock—cannot be bought on margin at all, or might require a 70% initial margin instead of 50% .

Brokers can also change these requirements at any time without giving you advance notice . If the market becomes extremely volatile, your broker might raise the maintenance requirement from 25% to 40% overnight. If your account doesn't have enough equity to cover this new requirement, you could face a margin call even if the stock price hasn't changed.

Step-by-Step: Opening and Using a Margin Account

Consent: You must sign a margin agreement. This is often a separate document or a specific section in your account application where you acknowledge the risks .
Deposit: You must deposit at least $2,000 to meet the minimum margin requirement .
Check Marginability: Not all stocks are "marginable." Penny stocks, IPOs, and certain low-volume over-the-counter (OTC) stocks usually require 100% cash .
Execute Trade: When you place a buy order, the broker automatically calculates how much of your cash to use and how much to lend you based on your settings.
Monitor Equity: You must regularly check your "Equity Percentage" to ensure you stay above the maintenance requirement.