Margin vs Portfolio Margin

What is the difference between margin and portfolio margin?

Standard margin and portfolio margin both set how much equity an account must hold against its positions, but in opposite ways. Standard Regulation T margin is strategy-based: it charges each position a fixed percentage or formula, generally 50 percent of a stock purchase up front and a 25 percent maintenance floor. Portfolio margin is risk-based: it reprices the whole account across stressed price scenarios and sets the requirement to the largest projected loss.

Standard margin is the default in nearly every retail brokerage account. Federal Reserve Regulation T sets the initial deposit, and FINRA states that a firm can lend up to 50 percent of the total purchase price of an eligible margin stock. FINRA rules then require equity in an account holding only margin stock to stay at or above 25 percent of the current market value of the long positions. Each position is charged on its own terms. Recognized structures get some relief, since a defined-risk spread is usually charged at its maximum loss, but an offsetting hedge held elsewhere in the account changes little.

Portfolio margin is permitted under FINRA Rule 4210(g). The firm reprices the whole account across a defined range of hypothetical market moves and sets the requirement to the largest loss that appears. Risk is treated as a property of the portfolio rather than of isolated legs, so a hedge that genuinely caps downside reduces the charge.

How margin and portfolio margin requirements are calculated

Under Reg T the arithmetic is fixed. Buy 200 shares at $100 for $20,000 of market value, deposit $10,000, and borrow $10,000. Equity equals market value minus the loan balance. Because the loan does not shrink when prices fall, equity absorbs the entire decline. The maintenance trigger sits where equity hits 25 percent, at $10,000 divided by 0.75, or $13,333 of market value, about $66.67 per share. At $60 the position is worth $12,000, equity is $2,000 or 16.7 percent, and the deficiency against the $3,000 required is $1,000.

Under portfolio margin the arithmetic is a stress test. The OCC Theoretical Intermarket Margin System values each underlying group at ten equidistant points across a band: plus or minus 15 percent for individual equity securities and narrow-based indexes, +6 percent to −8 percent for high-capitalization broad-based market indexes, and plus or minus 10 percent for the rest. The worst projected loss becomes the requirement, subject to a floor of $0.375 per listed option, unlisted derivative, or security future, multiplied by the contract multiplier.

Run a hedged book through the stress test. Hold 1,000 shares at $50 with ten standard $45 puts initially valued at $1. In the down-15% scenario, the shares fall to $42.50 and lose $7,500. If the puts reprice to $3, the hedge gains ($3 − $1) × 100 × 10 = $2,000, leaving a $5,500 scenario loss. Reprice each leg at every required valuation point, then apply the account’s offsets, minimums, and house charges to calculate portfolio margin. Compare that final requirement with the Reg T treatment: a $25,000 initial requirement on the stock, with the long puts paid in full.

How to choose between margin and portfolio margin

Account size decides eligibility first. Standard margin opens with modest equity, and FINRA states that $2,000 is the minimum needed to trade on leverage in a margin account. The $25,000 pattern day trader minimum is no longer a regulatory floor. FINRA Regulatory Notice 26-10 replaced the day-trade count designation and that threshold with intraday margin requirements effective June 4, 2026, under which equity must hold the 25 percent maintenance minimum throughout the trading day rather than only at the close. Firms may phase in the framework through October 20, 2027, so day-trading treatment on a specific account is firm specific during the transition. Portfolio margin is gated: FINRA interpretations set the floor at $100,000 where the firm has full real-time intraday monitoring and can reject an order that would create a deficiency, $150,000 to $500,000 where monitoring is partial, and $500,000 where it is absent. Unlisted derivatives require $5 million.

Position structure decides the modeled loss second. Protective puts and other eligible offsets reduce exposure under the stress scenarios. An unhedged stock position also receives a scenario-based charge, so the benefit is not limited to hedged books. Compare the final requirement after concentration and house charges with the standard-margin requirement.

Tolerance for moving requirements decides suitability third. A Reg T requirement on a stock position is static until the price moves or the firm raises its house requirement. A portfolio margin requirement is recomputed continuously as prices and volatility change, so a book that looks comfortable in calm conditions can demand more collateral when volatility rises or an option position approaches the strikes where its risk peaks.

Where margin and portfolio margin are the same

Neither method changes the quality of a trade. Both are collateral rules on borrowed capacity, and both scale outcomes in each direction. House requirements sit above the regulatory floor in both, and FINRA notes those requirements can exceed the Regulation T, FINRA, and exchange minimums and can change at any time without advance notice. A position can become deficient with no price move at all.

Portfolio margin has a regulatory deficiency deadline of three business days. That deadline does not grant an unconditional three-day holding period. The firm’s margin agreement governs its right to demand collateral or liquidate positions sooner.

Bottom line

Reg T margin prices each position with a fixed formula: 50 percent to establish, 25 percent to maintain, more if the house says so. Portfolio margin stress-tests the whole account, hedged and unhedged eligible positions alike, and charges the largest projected loss across a plus or minus 15 percent equity band. Compare both using your actual positions, account eligibility, and the broker’s final collateral calculation: eligible offsets improve capital efficiency, and concentration and house charges set the final requirement.