DEFINITION of 'Marginal VaR'
The additional amount of risk that a new investment position adds to a portfolio. Marginal VaR (value at risk) allows risk managers to study the effects of adding or subtracting positions from an investment portfolio. Since value at risk is affected by the correlation of investment positions, it is not enough to consider an individual investment's VaR level in isolation. Rather, it must be compared with the total portfolio to determine what contribution is makes to the portfolio's VaR amount.
BREAKING DOWN 'Marginal VaR'
An investment may have a high VaR individually, but if it is negatively correlated to the portfolio, it may contribute a much lower amount of VaR to the portfolio than its individual VaR. For example, consider a portfolio with only two investments. Investment X has a value at risk of $500 and investment Y has a value at risk of $500. Depending on the correlation of investments X and Y, putting both investments together as a portfolio might result in a portfolio value at risk of only $750. This means that the marginal value at risk of adding either investment to the portfolio was $250.