Margin Period of Risk (MPOR)

The margin period of risk, usually abbreviated MPOR, is the length of time that risk models assume will pass between the last exchange of collateral with a counterparty and the point at which that counterparty's position is fully closed out following a default. It is not a fixed calendar period observed after the fact; it is an assumption built into margin calculations, used to size how much collateral needs to be held at any moment to cover the price moves that could happen during that gap, before a replacement trade or liquidation can be completed.

MPOR sits at the center of how initial margin is calculated for both cleared and bilateral derivatives, and it interacts directly with collateral haircuts, since both exist to cover the same underlying problem: the time lag between when collateral was last confirmed adequate and when it might actually need to be sold or applied. The concept is used by central counterparties (CCPs), bilateral derivatives counterparties operating under credit support arrangements, and regulators setting minimum margin standards for uncleared trades.

Imagine a landlord who collects a security deposit from a tenant once a year, rather than checking the state of the apartment every single day. If the tenant causes damage the day after an inspection, the landlord will not find out, and will not be able to act, until the next scheduled check, nearly a year later. The deposit has to be large enough to cover whatever could go wrong in that entire gap, not just in the single day the damage happened.

The margin period of risk is that gap for a financial trade. It covers the time between the last moment a counterparty's collateral was confirmed sufficient and the moment, after a default is detected, that the position is finally closed out and replaced. Margin has to be sized for everything that could plausibly happen to prices during that whole window, which is why a longer gap, or a more volatile trade, calls for more collateral upfront.

A common simplified way to translate MPOR into a margin requirement scales a daily measure of risk by the square root of the number of days in the period, reflecting how uncertainty grows over a longer horizon:

Here $M$ is the margin requirement, $\sigma$ is the daily volatility of the exposure's value, $T$ is the margin period of risk measured in days, and $z$ is a confidence multiplier chosen to cover a given percentage of likely outcomes. For example, a position with daily volatility of 2 and an MPOR of 10 days, margined to a confidence multiplier of 2.3, would require:

Doubling the MPOR to 20 days would raise the requirement only to roughly $2 \times \sqrt{20} \times 2.3 \approx 20.6$, illustrating why a longer assumed gap increases required margin, but at a slower rate than the gap itself grows, because of the square-root relationship.

• How frequently collateral is exchanged: daily margin calls allow a shorter MPOR than weekly or less frequent exchanges.
• Whether the trade is cleared through a CCP, where standardized, short default-management timelines apply, or bilateral, where the process depends on the two counterparties' own contractual terms.
• The liquidity of the underlying instrument, since illiquid products take longer to novate or replace after a default, extending the effective close-out period.
• Dispute risk: if a counterparty's margin calls are frequently disputed or delayed, regulators and risk models typically extend the assumed MPOR to compensate.

CCPs generally assume a short MPOR, often measured in a small number of days, because cleared markets have standardized default-management procedures and daily margin calls. Bilateral, uncleared derivatives, margined under an independent amount and variation margin framework, are typically assumed to need a longer MPOR, reflecting slower, less standardized close-out processes, which is one reason regulatory initial margin requirements for uncleared trades tend to be larger than for equivalent cleared trades.

Minimum MPOR assumptions for regulatory margin calculations are set out in rules developed by the Basel Committee on Banking Supervision and the International Organization of Securities Commissions, and implemented through national frameworks such as the Dodd-Frank Act in the United States and MiFID II in Europe. CCPs' own MPOR assumptions are reviewed by regulators under standards such as the Principles for Financial Market Infrastructures (PFMI).

• Basel Committee on Banking Supervision
• International Swaps and Derivatives Association (ISDA)