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Quantitative Finance · Glossaire

Qu'est-ce que « Value at risk » ?

Definition 21.2 Rates, Credit, XVA and Risk · Chapitre 21 — Market-Risk Measures

The value at risk of a portfolio at confidence level α\alpha over a horizon hh is the α\alpha-quantile of its loss L=−ΔVL = -\Delta V over hh: VaRα=inf⁡{ℓ:P(L>ℓ)≤1−α}\mathrm{VaR}_\alpha = \inf\{\ell:\P(L>\ell)\le1-\alpha\}. At 99% over one day it is a loss exceeded on one day in a hundred.

Exemples

Example 21.3 (The book)

A small USD book on 23 September 2026: long USD 200 million of a ten-year Treasury par bond, short USD 300 million of a two-year, long EUR 100 million, short JPY 5 billion, and short a three-month at-the-money EURUSD straddle on EUR 400 million (implied volatility 8%, held fixed). Its four risk factors are the daily changes in the two- and ten-year par yields (4.85% and 5.11% that day) and the log returns of EURUSD (1.1411) and USDJPY (157.92). Their EWMA daily volatilities are 6.4 and 5.7 basis points, 0.28% and 0.65%.

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