Portfolio Margin vs Reg T: How the Requirement Is Set

$25,000 or $7,500. Those are the two numbers a broker could ask you to hold against the same $50,000 of stock, depending on which margin method the account uses. The gap explains why portfolio margin is popular with active options traders. It also explains how accounts on it get into trouble.

How does Reg T set the requirement?

By formula, one position at a time. The Federal Reserve Board’s Regulation T asks you to put up half the price of a marginable stock when you buy it. FINRA Rule 4210 then sets the floor you must keep while you hold it, at least 25% of the market value for long stock, and most brokers set a house figure above that. Initial margin and maintenance margin each have their own page.

Options get their own fixed formulas under the same approach, usually called strategy-based margin. A covered call, a spread and an uncovered put each have a set calculation, and the system looks at each strategy separately.

The method is simple to check by hand. It barely notices hedges, though. A stock and the put protecting it are treated largely as two separate positions, so the opening requirement on the stock is the same with or without the put.

How does portfolio margin set it?

By simulation. FINRA Rule 4210(g) allows a broker to set requirements from a pricing model that revalues every position in the account at a series of hypothetical prices, and for an individual stock those prices run from 15% below the current price to 15% above it. The largest loss the model finds across that range becomes the requirement.

The whole account is stressed together. A stock and its put move through the same price points, so the gain on the put offsets part of the loss on the stock before any number is produced, which is the reason hedged and balanced accounts tend to need much less equity under this method.

The same position under both methods

Start with no hedge. A hypothetical account buys 1,000 shares at $50.

Under Reg T you open the position with $25,000 of your own money. Under portfolio margin, in an account that already meets the minimum equity, the model asks for $7,500. That means $50,000 of stock can sit on $7,500 of equity, roughly 6.7 times leverage, against 2 times at the Reg T opening figure.

Now read the same number the other way. If the requirement is $7,500 and you hold only that much equity, a 15% fall uses up all of it. Somewhere before that point the broker calls for more.

Add a hedge. The account buys 10 puts with a $45 strike for $1.00 each, $1,000 in total.

Portfolio margin sees that offset and asks for no more than $6,000. Reg T’s opening requirement on the stock is still $25,000, and the puts must be paid for in full on top. The options break-even calculator shows where a put like this starts to pay at expiry.

	Reg T (strategy-based)	Portfolio margin
Who sets the method	Federal Reserve Board, FINRA Rule 4210	FINRA Rule 4210(g), broker’s model
How it is worked out	Fixed percentage per position or strategy	Largest loss across a price range
Range for individual stocks	Not used	Plus and minus 15%
Credit for hedges	Limited	Built in
Minimum equity	Set by broker	$100,000 under FINRA, often higher at brokers
How often it changes	When prices change	When prices or volatility change

Where does the margin call land?

Lower, if you borrow the same amount. Much closer, if you borrow what the model allows.

Keep the unhedged 1,000 shares and assume, for simplicity, that the requirement stays at 15% of market value at every price and the broker adds nothing on top. The call comes when equity falls to the requirement.

Same stock. With the Reg T-sized loan, portfolio margin moves the call price down by almost $4, and that’s a real cushion. Borrow the $40,000 the lower requirement makes possible and the call sits at $47.06, a fall of under 6% from $50, which an ordinary stock can manage in a single bad session without any news at all. The margin call calculator runs the Reg T version for any position.

Who qualifies?

The FINRA floor is $100,000 of account equity. Brokers commonly set their own minimum above that, ask for approval at their higher options levels, and require a separate agreement with a risk disclosure you sign.

The method suits accounts that hold offsetting positions: stock with protective puts, spreads across strikes, short options balanced by long ones. A portfolio of unhedged stocks still gets a lower number than Reg T, but the saving comes from leverage alone. Leverage magnifies losses as much as gains.

What can go wrong with portfolio margin?

The requirement moves. A model that prices options reacts to volatility, so a quiet week followed by a sharp one can raise the number on positions you never touched. Selling puts on margin walks through how fast a short option’s requirement can grow when the stock falls.

Brokers add charges the bare rule does not. Concentrated positions, small and thinly traded stocks, and holdings that gap often draw extra requirements on top of the model’s figure. They can be large. They can also arrive overnight.

Calls arrive faster in practice. With more leverage in place, a fall that would have been a nuisance at Reg T can become a demand for cash within days, and if the account cannot meet it the broker can sell positions to cover, in whatever order and at whatever prices it chooses.

Which one fits your account?

Reg T fits most accounts. It is easy to work out, harder to over-borrow under, and a stock-only investor gains nothing but extra borrowing room by switching.

Portfolio margin fits an account that already hedges and wants the requirement to reflect it. Use it for the lower number on hedged positions. Treat the extra borrowing room as a hazard.