Portfolio Margin vs Reg T: How Risk-Based Margin Changes Your Options Buying Power

Two brokerage accounts can hold the same options position and be charged very different amounts for it. Sell one put 10% below a broad index at 6,000 and the standard formula asks you to post about $54,600 per contract. Run the same put through portfolio margin and the requirement is about $7,000, roughly 7.8 times less in our illustrative math. Nothing about the trade changed. Only the method did: one is a fixed recipe written for single positions, the other a stress test of the whole account. New to the vocabulary? Our options glossary defines uncovered options, assignment and margin in plain terms.

That gap is why active option sellers ask for portfolio margin, and why risk managers worry about it. This guide works through both systems with the actual rule text: how Reg T and FINRA’s strategy-based formulas set requirements, how the portfolio margin stress test works, how much it saves on six common positions, who qualifies, and how the extra buying power turns a 5% selloff into a margin call. The rules are current to FINRA’s 2026 intraday margin changes.

What is the difference between Reg T and portfolio margin?

Reg T margin sets requirements position by position with fixed percentages, while portfolio margin stress-tests the whole account and charges for its largest modeled loss. The first asks “what kind of position is this?” The second asks “what does this account lose if the market moves?”

“Reg T” is shorthand for two layers. Regulation T is the Federal Reserve’s rule on broker credit (12 CFR Part 220). It sets the 50% initial margin to buy a margin equity security and 150% on a short sale, counting the sale proceeds, and for listed options it defers to the rules of the exchanges and FINRA (12 CFR 220.12). FINRA Rule 4210 then adds the maintenance requirement, 25% of long margin securities, a $2,000 minimum equity to use leverage, and the detailed option formulas. Together they are called strategy-based margin: each recognized strategy has its own recipe.

Portfolio margin is the alternative written into FINRA Rule 4210(g). Positions on the same underlying are grouped, revalued by an approved pricing model at ten points across a stress range, and the worst result becomes the requirement. Regulation T itself states that it does not apply to accounts that comply with a portfolio margining system approved by the SEC, which is why a portfolio margin account can ignore the 50% rule on stock (12 CFR 220.1(b)(3)).

How does Reg T strategy-based margin calculate options requirements?

Strategy-based margin applies a fixed formula to each option position: long options are paid in full, uncovered short options carry the option’s value plus a percentage of the underlying, and recognized hedges get reduced charges. The formulas live in FINRA Rule 4210(f)(2), because Regulation T leaves listed options to the self-regulatory organizations.

1. Long options. Options expiring in nine months or less must be paid for in full. Listed options with more than nine months left can be bought on margin at 75% of their value, which is why long-dated calls get some loan value.
2. Uncovered short equity options. 100% of the option’s current value plus 20% of the underlying stock’s value, minus any out-of-the-money amount, with a floor of the option value plus 10% of the stock (for puts, 10% of the strike).
3. Uncovered broad-index options. The same structure at 15% of the index value, with the same 10% floor.
4. Short straddles and strangles. The larger of the put or call requirement, plus the current value of the other option.
5. Spreads. The lesser of the uncovered requirement or the spread’s maximum potential loss, computed at every strike in the spread; the long leg is paid in full.
6. Covered calls and collars. No margin on a call written against stock you hold; a collar with the put below the call and the same expiry cuts the stock’s maintenance to the lesser of 10% of the put strike plus its out-of-the-money amount, or 25% of the call strike.

Take a $200 stock and an uncovered 180 put worth $2.34. The formula is $234 + max(20% × $20,000 − $2,000 out-of-the-money, 10% × $18,000) = $2,234. That is predictable and easy to check by hand, which is its main virtue. Its weakness is that it cannot see across strategies: a short put, a long put two strikes lower in a different expiry and some stock are each charged separately unless they fit one of the patterns the rule recognizes. If you sell puts this way, the cash-secured put and wheel guide shows the fully funded version, which needs no margin model at all.

How does portfolio margin calculate the requirement?

Portfolio margin groups every position by its underlying, revalues the group at ten equally spaced price points across a fixed stress range, and charges the largest loss. Gains and losses inside a group net fully at each point, so a hedge counts dollar for dollar whether or not it matches a textbook strategy.

The stress range depends on what the underlying is. Rule 4210(g)(2)(F) sets three:

For each group the requirement is the greater of the worst loss across the ten points or $0.375 per contract times the multiplier, which is $37.50 on a standard 100-share option. Groups are summed, with limited offsets between related index groups as SEC Rule 15c3-1a allows. The values come from a theoretical pricing model that must be approved; when the SEC approved customer portfolio margining for equities in December 2006, it noted that the only qualifying model was the Options Clearing Corporation’s Theoretical Intermarket Margining System (TIMS) (SEC Release 34-54918). That approval took effect on April 2, 2007.

Chart 1 shows what the stress window sees and what it doesn’t. The 10%-out-of-the-money index put is still out of the money at the worst tested point, −8%, so the modeled loss there is only about $7,000. The strategy-based formula, by contrast, charges about $54,600, enough to absorb an instant drop of roughly 19.5%. Neither number is a forecast. They are two different answers to “how much cushion should this trade carry?”, and portfolio margin’s answer stops at the edge of its window.

How much less margin does portfolio margin require?

On hedged stock and short index premium, portfolio margin cut requirements by roughly 70% to 87% in our illustrative math; on defined-risk spreads and uncovered single-stock options the cut is closer to half. The saving depends on how much of the formula’s charge is above the loss the stress test can actually find.

Three patterns stand out. First, hedges get paid: stock plus a protective put drops from about $10,200 to $1,850 because the model can see that the put caps the loss, which the 50% rule cannot. That is why portfolio margin suits the collar on a concentrated position, where the hedge is the point. Second, defined-risk trades gain less than you might expect in dollars: a $10-wide spread can never lose more than $1,000, so there is little excess for the model to remove, which is why the economics in our credit spread guide barely change. Third, short index premium gains the most, because the index window is narrow (−8%) and an out-of-the-money put barely moves inside it.

That third pattern is also where the trouble starts. A $250,000 account can sell about four of those index puts under the formula, or about thirty-five under portfolio margin. Nothing in the rule tells you which number is prudent.

Who qualifies for portfolio margin?

You need a non-IRA margin account, approval to write uncovered options, a signed portfolio margin risk disclosure, and equity above your broker’s minimum, which FINRA does not let fall below $100,000. The broker also needs FINRA approval of its own portfolio margin methodology before it can offer the account.

• Not an IRA. Rule 4210(g) says plainly that its portfolio margin provisions do not apply to Individual Retirement Accounts.
• Uncovered options approval. Only customers approved for uncovered short options under FINRA Rule 2360 may use a portfolio margin account (Rule 4210(g)(5)(B)).
• Disclosure. Before the first trade, the firm must give you a written statement on the risks of portfolio margining and get your signed acknowledgment.
• Separate account. Portfolio margin runs in its own account or clearly identified sub-account; a deficit there cannot be covered by excess equity in another account without an actual transfer, unless it is a sub-account of the same margin account.
• Minimum equity. Set by the broker, within floors FINRA sets by how well the firm monitors risk during the day.

The practical gate is usually the broker, not FINRA. Firms set their own minimums above these floors, may require an options track record, and can withdraw portfolio margin if equity falls below their threshold. For executives with concentrated stock, note that Rule 4210(g)(1)(I) requires brokers to monitor concentrated positions, and house policies commonly charge extra for them, so a portfolio built around one employer stock often sees a much smaller benefit than the table above suggests.

Should you switch to portfolio margin?

Switch if your book is mostly hedged or short premium on broad indexes, you qualify, and you will hold the same positions with less capital; don’t if the main appeal is selling more. Portfolio margin is a better measuring tape. It does not make any position safer.

The questions in Chart 3 sort most readers quickly. If the account is an IRA, the answer is no by rule. If most of the capital is long stock with a few covered calls, the saving is real but the stock itself is the risk, and our options portfolio structure guide is the better place to start. The hard case is the experienced premium seller with a large taxable account, because that reader will qualify and will see the biggest headline saving.

For that reader, the right test is behavioural. Write down your maximum requirement use before you apply. We cap it at about 50% of equity in any account that sells premium, and we size each short position to a move beyond the stress window: a −16% to −20% index day, or a −30% single-stock gap on earnings. If you can follow those caps, portfolio margin turns the capital you no longer have to post into a cash buffer and a hedge budget. If you can’t, it hands you more rope.

How can portfolio margin turn a selloff into a margin call?

Portfolio margin requirements are recalculated from the current price and volatility, so in a selloff the stress window slides down with the market, implied volatility rises, and the requirement can triple while equity falls. Strategy-based requirements rise too, but they start far above the modeled loss, which leaves more room.

The worked example behind Chart 4: a $250,000 portfolio margin account sells ten 5,400 puts on a broad index at 6,000, collecting about $5,900. The opening requirement is about $70,400, or 28% of equity. That looks conservative: it is under a third of the account’s portfolio margin capacity. Yet ten contracts is two and a half times the four the strategy formula would allow. Now let the index fall while implied volatility rises from 18% to 30%:

The deficit appears at about a 5% decline, a decline that needs no crisis to happen. By −10% the puts have lost about $207,000, 83% of the account, and the requirement is six times what it was. The same trade at four contracts, the strategy-based capacity, loses about $83,000, or a third of the account: painful, but survivable. At twenty contracts, still only 57% of the portfolio margin capacity on day one, the −10% loss is about $415,000, more than the account holds, and you would owe the broker the difference.

Two features make this worse in practice. Brokers’ models may also stress volatility and add charges for concentration and liquidity, so real requirements rise faster than the price-only math here. And on a fast day the broker does not have to wait for you: account agreements typically allow liquidation without notice, at the worst prices of the move. The same dynamic is why we size short straddles and strangles to the largest past earnings move, not to the margin charge.

What happens when you miss a margin call under each system?

Under portfolio margin you have three business days to fix a deficiency before the broker must stop new opening trades and liquidate; under Reg T an initial call is due within one payment period and a maintenance call within 15 business days at most. Those are regulatory outer limits; your broker’s agreement can, and in volatile markets usually does, act much faster.

• Reg T initial (federal) call. Created when a new purchase or short sale is not fully margined. It must be met within one payment period (12 CFR 220.4(c)(3)), which Regulation T defines as the standard settlement cycle plus two business days, so currently three business days on a T+1 cycle.
• Maintenance call (strategy-based). Rule 4210(f)(6) requires margin to be obtained as promptly as possible and in any event within 15 business days, unless FINRA grants more time.
• Portfolio margin deficiency. Rule 4210(g)(10) gives three business days to deposit funds or securities or to hedge. After that the broker may accept only risk-reducing opening orders and must liquidate enough to bring the requirement back within equity. If it isn’t met by the next business day, the firm takes a net capital charge, which is why brokers move fast.
• Habitual liquidation. Firms must flag accounts that routinely meet portfolio margin deficiencies by selling positions rather than depositing funds, and act on them.

The practical difference is the starting point. A strategy-based account opens each position with a cushion far above the modeled loss, so it reaches a deficiency later. A portfolio margin account sized near its limit has almost no cushion, so the same move reaches the deadline sooner.

How do FINRA’s 2026 intraday margin rules change the picture?

FINRA’s new intraday margin standards replaced the pattern day trader rule and its $25,000 minimum in all regular margin accounts, effective June 4, 2026, but portfolio margin accounts are outside the new intraday calculation and keep their own intraday requirement. Brokers can phase the change in until October 20, 2027, so your firm may still be on the old rules (FINRA Regulatory Notice 26-10).

Under the new standard, a strategy-based margin account must hold its maintenance requirement throughout the trading day, not just at the close. If a trade leaves equity short of what the open positions require, the account has an intraday margin deficit that must be met as promptly as possible; FINRA’s investor guidance says repeated failures can restrict the account for up to 90 days. The $2,000 minimum equity to trade on margin still applies, and FINRA notes the rule covers margin used for zero-day options, the subject of our 0DTE guide.

The new deficit calculation excludes portfolio margin accounts. Instead, Rule 4210(g)(1)(K) requires brokers to make any portfolio margin account with less than $5 million in equity hold margin for intraday risk that is substantially similar to its end-of-day margin. In plain terms, opening and closing a large short-premium position within the day does not escape the stress test.

For someone choosing between the two, the 2026 change narrows one old argument for portfolio margin: you no longer need it, or $25,000, simply to day trade. The remaining reasons are the ones in this guide: hedge recognition and capital efficiency for an options book that is large and actively risk-managed.

How should you run a portfolio margin account?

Run it on your own risk limits, set tighter than the margin rule, and check the stress test you care about every day. The routine we use:

1. Cap requirement use at about 50% of equity in any account that sells premium; treat 35% as the level where you stop adding.
2. Run your own stress at twice the rule’s window (−16% to −20% for index books, −30% for single names) with implied volatility up 10 points, and keep that loss below half of equity.
3. Check direction: if every short option loses in the same move, count them as one position when you size.
4. Price hedges into the trade: a long put or call spread that turns an uncovered position into a defined-risk one usually costs little under portfolio margin and caps the tail the model ignores.
5. Keep a cash buffer of at least 10% of equity outside any position, so a deficiency can be met by deposit, not liquidation.
6. Know your broker’s house rules: concentration add-ons, event charges around earnings, and when it will liquidate without notice.
7. Review margin on box spreads and synthetics separately; brokers treat these offsetting structures differently, as our put-call parity guide explains, and FINRA’s strategy formula charges a long European-style box 50% of its strike width.

Portfolio margin is one of the most useful tools an options investor can have, and one of the easiest to misuse. Measured honestly, it lets a hedged book carry the same risk with a fraction of the capital. Treated as buying power, it makes a 5% selloff a margin event. The rule only measures risk inside its window; outside it, the sizing is up to you.

Frequently asked questions

Key takeaways

1. Reg T, together with FINRA Rule 4210’s strategy-based formulas, charges each position by a fixed recipe: 50% to buy stock, and option value plus 20% of the stock, less any out-of-the-money amount, for an uncovered equity option.
2. Portfolio margin revalues the whole account at ten points across a stress range (±15% for single stocks, +6%/−8% for high-cap broad indexes) and charges the worst loss, with full netting inside each underlying.
3. The biggest savings come on hedged stock and short index premium; our illustrative 10%-out-of-the-money index put needs about 7.8 times less under portfolio margin. Defined-risk spreads save far less.
4. Eligibility needs uncovered-options approval, a broker minimum of at least $100,000, and a non-IRA account.
5. Portfolio margin requirements expand fast in a selloff because the stress window moves with the market and volatility rises; size to a move beyond −8% or −15%, not to the buying power.
6. Treat the freed capital as a buffer or a hedge budget. We keep requirement use below about half of equity in any account that sells premium.

Sources and method

1. FINRA Rule 4210, Margin Requirements — Maintenance margin, option formulas in (f)(2), portfolio margin in (g): stress ranges, ten valuation points, $0.375 minimum, IRA exclusion, deficiency timelines
2. FINRA, Interpretations of Rule 4210 — Interpretation 4210(b)(4)/034, minimum equity for portfolio margin accounts; Reg T exclusion for portfolio margin accounts
3. FINRA Regulatory Notice 26-10 (April 2026) — Intraday margin standards replacing the pattern day trader rules; effective June 4, 2026, phase-in to October 20, 2027
4. 12 CFR § 220.12, Regulation T margin requirements (Cornell LII) — 50% initial margin on margin equity securities, 150% on short sales, options deferred to exchange rules
5. 12 CFR § 220.1, Regulation T scope (Cornell LII) — Reg T does not apply to accounts that comply with an SEC-approved portfolio margining system
6. SEC Release No. 34-54918 (December 12, 2006) — Approval of customer portfolio margining for equities, effective April 2, 2007; OCC’s TIMS as the qualifying pricing model

All position values, requirements and account paths in this article are illustrative Black–Scholes calculations, not quotes or any broker’s actual requirement. Single-stock examples use a hypothetical $200 stock at 35% implied volatility with 45 days to expiry and a 4% rate; index examples use a hypothetical high-capitalization broad index at 6,000 (multiplier 100) at 18% implied volatility. Portfolio margin figures revalue positions at the ten points in FINRA Rule 4210(g) with prices only; real broker models may also shift volatility and add house charges for concentration, liquidity and events, which raise requirements. Rule references are as of October 1, 2026. This is general information, not tax, legal or investment advice; confirm your own requirements with your broker.