Annual Rate of Occurrence
Free Annual Rate of Occurrence calculator with clear step-by-step results.
About Annual Rate of Occurrence
Annualized rate of occurrence normalises threat frequency per asset.
Formula
Formula
ARO = events per year ÷ assets
Worked example
With the default values below, Annual Rate of Occurrence returns Annualized Rate of Occurrence of 0.02. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Expected events per yearminimum 0
- 2
- Assets exposedminimum 1
- 100
Results
- Annualized Rate of Occurrence
- 0.02
- Events per Asset
- 0.0200
- Frequency Label
- About once every 50 years per asset
Step by step
- 1Values used
- 2Formula
- 3Annualized Rate of Occurrence= 0.02
- 4Events per Asset= 0.0200
- 5Frequency Label= About once every 50 years per asset
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or fees or charges into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How does this calculator work?
Annualized rate of occurrence normalises threat frequency per asset.
Why does this matter?
Used inside ALE = ARO × SLE.
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