SPAN margin vs Reg-T
Explain SPAN margin and how it differs from the Reg-T margin used in stock accounts.
Lesson path
Futures, Indices, and Commodities
Futures Basics
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Explain SPAN margin and how it differs from the Reg-T margin used in stock accounts.
Risk-based margin vs flat-percentage margin
Stocks and futures both use the word 'margin,' but the underlying systems are very different. Stocks use Reg-T, set by the Federal Reserve in Regulation T — a flat percentage of position value. Standard Reg-T initial margin is 50 percent: a $10,000 stock position needs $5,000 of capital. Maintenance is typically 25 percent. Simple, blunt, asset-by-asset.
Futures use SPAN — Standard Portfolio Analysis of Risk. CME developed it in 1988 and most futures exchanges worldwide use it now. SPAN doesn't care about a flat percentage. It asks a different question: 'If price and volatility moved against this position in plausible ways tomorrow, what's the worst one-day loss?' Then it requires you to post enough margin to cover that worst-case scenario.
Practical numbers: an ES contract at 5,200 represents about $260,000 of notional S&P 500 exposure. Under Reg-T-style margin, you'd post around $130,000 (50 percent) to control that exposure. Under SPAN, the initial margin is roughly $13,000 to $15,000 — about 5 percent of notional. That's a huge capital efficiency difference, and it's the main reason institutional traders use futures for index exposure rather than buying the underlying basket of stocks.
What this means for you: SPAN's lower margin requirement is what gives futures their reputation for high leverage. Same exposure, far less capital tied up. The flip side is that the same percentage move costs the same dollar amount whether you posted Reg-T or SPAN — losses scale with notional, not with the margin you posted. SPAN doesn't make trades safer. It just lets you participate at smaller account sizes. That's why position sizing by risk-per-trade matters more in futures than anywhere else. With Reg-T leverage, sloppy sizing hurts. With SPAN leverage, sloppy sizing ends accounts.
Recap: SPAN is risk-based, Reg-T is flat-percentage. Same exposure costs about 5 percent of notional in SPAN versus 50 percent in Reg-T. Use the capital efficiency responsibly — losses still scale with notional.
Knowledge check
Answer before moving on.
1. What's the core difference between SPAN and Reg-T?
2. Why does SPAN typically require less capital for the same dollar exposure as Reg-T?
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