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Historical-simulation value at risk: data and rank convention

A historical-simulation calculation needs a loss record and a stated rule for selecting its empirical quantile.

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State which losses the record represents

A set of past realised portfolio returns is not automatically the historical repricing loss distribution of today’s holdings. In a historical-simulation model, identify the current exposure record and how observed factor changes are applied. Keep nonlinear repricing and any approximation explicit.

Choose an empirical quantile convention

For an equal-weight record of n losses sorted ascending, this page’s lower-quantile convention selects rank ceil(nc), counting from one. The public discrete tool can inspect an already supplied loss record; it does not reconstruct current holdings or run a historical repricing engine.

Inspect an original equal-weight record

For twenty equally weighted hypothetical losses 1 through 20, 95% confidence gives rank ceil(20×0.95)=19 and VaR 19. The worst 5% mass is the final observation, giving expected shortfall 20. These invented values are not market data.

Original equal-weight comparison
ConfidenceLower-quantile rankVaRExpected shortfall
90%181819.5
95%191920

Review data before calling it evidence

Record dates, missing-data handling, weights, horizon, pricing basis and sample convention. An observed record can omit severe events or reflect a different regime. Neither a correct rank nor a large sample guarantees future tail coverage.

Further references