Futures margin (performance bonds)

Definition

Futures margin is a good-faith performance bond, not a down payment and not borrowed money: initial margin is the deposit required to open a position, maintenance margin is the minimum equity that must be sustained while it is open. Requirements are set by the exchange/clearinghouse (with brokers free to require more) and are computed by portfolio risk systems (CME’s SPAN family) rather than as a fixed percentage of price.

How it works / structure

• Initial vs maintenance: open at ≥ initial; if account equity attributable to the position falls below maintenance, a margin call demands restoration to the initial level.
• Risk-based computation: SPAN-class systems scan scenarios (price moves, volatility moves) across a portfolio and charge the worst-case one-day loss; offsetting positions (calendar spreads, inter-market spreads) receive margin credits.
• Daily interaction with settlement: variation margin (ms-settlement) moves cash daily; margin requirements are re-evaluated on the post-settlement position.
• Requirement changes: exchanges raise margins in volatile markets, sometimes intraday — a position that was adequately funded can become under-margined with no price change.
• Simulation parameters: per-contract initial/maintenance levels, spread credits, a margin-call rule (restore-to-initial), and a forced-liquidation rule for unmet calls.

When it applies

Every futures and short options-on-futures position. Margin math determines maximum position size, cash reserve requirements, and the distance-to-liquidation that a risk plan must respect (risk-fixed-fractional sizes from risk, never from margin capacity).

Risk profile & failure modes

• Losses beyond the deposit: margin is a fraction of notional, so adverse moves can cost multiples of the posted bond (stated in the CFTC’s education materials).
• Forced liquidation at the low: unmet calls are closed by the broker at prevailing prices — mechanically selling into adverse moves.
• Margin-hike spirals: exchanges raising requirements during stress forces deleveraging exactly when liquidity is worst.
• Spread-credit fragility: legs of a spread can be liquidated separately, and the margin credit assumes the spread relationship holds — it can widen catastrophically in stress.

Evidence & limits

Margin mechanics and SPAN methodology are clearinghouse rules and published documentation, not hypotheses. Historical margin levels change over time; backtests must use period-appropriate requirements or state that they approximate.

Falsifiable-thesis examples

Illustrations only, not signals:

• “Position P, funded with 3x its initial margin in reserve, will survive the next quarter without a margin call under exchange requirements as of today” — falsified by any call in replay.
• “Exchange initial margin on contract X will be raised at least once within 90 days” — falsified if no increase is published in the window.

Cross-references

• Instrument basics: instrument-futures-contract, instrument-futures-option
• Cash mechanics: ms-settlement
• Sizing discipline: risk-fixed-fractional, risk-max-drawdown-budget
• Securities-account margin (different system): acct-margin-rules