SPAN Margin Methodology Explained

Key Takeaways

• SPAN sets initial margin by simulating a portfolio across a fixed grid of price and volatility scenarios, then charging the worst plausible one-day loss.
• The core tool is the risk array: 16 scenarios per contract that shift the underlying up and down and raise or lower volatility.
• Margin under SPAN is a performance bond held by the clearinghouse to cover a default, not a partial payment or a loan.
• Because it nets offsetting positions, SPAN often charges far less than the sum of margins on each leg treated alone.

What It Is

SPAN was developed by the Chicago Mercantile Exchange in 1988 and is now licensed to clearinghouses and exchanges around the world. It is a portfolio-based margin model: rather than margining each position in isolation, it looks at how every contract in an account would gain or lose together under a common set of market moves.

The output is a single number, the SPAN requirement, which becomes the account's initial margin. The clearinghouse collects it up front from every clearing member as protection. If a member defaults, that margin, plus daily variation margin and a guaranty fund, is what stands between one failure and losses spreading to everyone else.

The Intuition

A plain futures contract can lose money in only one direction at a time, but a real book mixes longs, shorts, calls, and puts across several months and products. Charging the full risk of each leg separately would wildly overstate the danger, because a loss on one leg is often a gain on another.

SPAN asks a sharper question: if the market moved hard tomorrow, what is the most this entire portfolio could lose? It answers by testing the book against a menu of standardized shocks and taking the ugliest result. That worst case, not the notional size of the trades, is what the clearinghouse needs covered.

How It Works

For each contract, SPAN builds a risk array of 16 scenarios. Seven price points are tested: unchanged, plus and minus one-third, two-thirds, and the full price scan range, which is the exchange's estimate of a large one-day move. Each of those seven is paired with volatility moving up and down, giving 14 scenarios. Two more extreme scenarios move the price far beyond the scan range but count only a fraction of the resulting loss.

The largest loss across those 16 scenarios is the scan risk. SPAN then adjusts it:

• An intra-commodity (calendar) spread charge is added, because the grid assumes all months move in parallel and real calendar spreads do not.
• A spot or delivery-month charge is added for contracts near expiration, where prices move more sharply.
• An inter-commodity credit is subtracted for offsetting positions in correlated products, such as related energy or grain contracts.
• The result is compared with a short option minimum, and the larger of the two is taken.

That final figure is the SPAN requirement, and it becomes the initial margin the account must hold.

Worked Example

A trader is long one crude oil futures contract. The contract covers 1,000 barrels, so each dollar per barrel of price movement is worth 1,000 dollars. The exchange has set the price scan range at 5.00 dollars per barrel.

For a plain long future the profit and loss is linear, and volatility shifts do not change it, so the worst standard scenario is the full down move:

• Down the full scan range: 5.00 dollars x 1,000 barrels = a 5,000 dollar loss.

Now the extreme down scenario. SPAN moves the price three times the scan range but counts only 35 percent of the loss:

• 3 x 5.00 dollars = 15.00 dollars per barrel x 1,000 barrels = 15,000 dollars, then x 0.35 = a 5,250 dollar loss.

The scan risk is the largest loss across all scenarios, so it is 5,250 dollars, not 5,000. With a single contract there are no spreads to add and no options, so the short option minimum does not bind. The SPAN requirement, and therefore the initial margin, is 5,250 dollars. Notice the extreme scenario set the number: at three times the range and 35 percent coverage it slightly exceeds the full standard move.

Common Mistakes

1. Treating SPAN margin as a down payment. It is a good-faith deposit held by the clearinghouse, refunded when the position is closed, not equity you are buying.
2. Assuming initial margin is fixed. Exchanges widen the price scan range when volatility rises, so the same position can require more margin overnight.
3. Confusing initial margin with variation margin. SPAN sets the initial buffer; variation margin is the separate daily cash that settles actual gains and losses.
4. Expecting your broker's number to match the exchange minimum. Brokers routinely add a house margin on top of the clearinghouse SPAN requirement.
5. Forgetting the offsets. Adding a hedging leg can lower a portfolio's SPAN requirement rather than raise it, because credits reduce the scanned loss.

Frequently Asked Questions

Q: What is span margin in one sentence? It is initial margin calculated by a risk-array model that scans a portfolio of futures and options against a grid of price and volatility scenarios and charges the worst likely one-day loss.

Q: Who sets the span margin requirement on my account? The clearinghouse and exchange set the scenario parameters and the resulting minimum, but your broker can require more. The number you post is usually the exchange SPAN requirement plus any house add-on.

Q: How is SPAN different from Regulation T stock margin? Regulation T charges a flat percentage of position value, typically 50 percent initial for stocks. SPAN is risk-based and portfolio-wide, so a well-hedged book can be margined at a small fraction of its notional size.

Q: Does span margin change from day to day? Yes. When markets get more volatile the exchange widens the price scan range, which increases the scanned loss and raises the requirement, even if you have not touched the position.

Q: What is SPAN 2? SPAN 2 is the newer CME framework that layers historical value at risk and stress analysis onto the original scenario approach, giving a more granular view of portfolio risk while keeping the same performance-bond purpose.

Sources

1. CME Group. "SPAN Methodology Overview." https://www.cmegroup.com/solutions/risk-management/performance-bonds-margins/span-methodology-overview.html
2. CME Group. "CME SPAN 2 Margin Framework." https://www.cmegroup.com/clearing/files/cme-span-2-margin-framework.pdf
3. Investopedia. "SPAN Margin." https://www.investopedia.com/terms/s/spanmargin.asp
4. CME Group. "Performance Bonds/Margins." https://www.cmegroup.com/solutions/risk-management/performance-bonds-margins.html

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.