An @RISK alternative that opens your @RISK workbooks

Guide · Updated October 2026

xellstorm runs Monte Carlo simulations of Excel models in the browser, and it opens a workbook built for @RISK as it is: it reads 53 of @RISK’s distribution functions and 47 of its percentile forms, with their parameters still linked to your cells, along with RiskOutput, RiskCorrmat and RiskSimtable. It needs neither @RISK nor Excel, on Windows, macOS or Linux.

Your workbook is not changed, so the model still opens in @RISK. Before you run, the import lists what it converted and every formula it left, with the reason.

Download an example written for @RISK (.xlsx) Open your workbook in the app

@RISK and xellstorm side by side

	@RISK	xellstorm
Where it runs	Inside Excel for Windows; on a Mac, only by running Windows on it	In a browser on Windows, macOS or Linux; Chrome and Edge recommended
Installation	An add-in on every computer that runs the model	None, and no admin rights
Your workbook	@RISK functions in the cells; without @RISK they do not calculate	Read as it is: xellstorm writes nothing into it
Colleagues	Need @RISK to rerun the model	Open it in the browser; report readers need no license
Where it calculates	On your computer, in Excel	On your computer, in the browser tab; the workbook is never uploaded

What the table says about @RISK follows its vendor’s published installation notes as of October 2026; check the current requirements with the vendor.

Which @RISK functions convert

The tables are generated from the importer’s own rule list, so they are exactly what it converts. Each function maps to the distribution it describes, with its parameters translated as @RISK documents them, and each mapping is tested against the equivalent scipy distribution. “Percentiles” marks the …Alt and …AltD forms, which give a distribution by its percentiles: xellstorm solves for the distribution exactly when you run. † marks the functions that convert with numbers only.

@RISK distribution functions the importer converts, by distribution († numbers only: the parameters are computed from the arguments)
Distribution (xellstorm name)	@RISK
Bernoulli `bern`	`RiskBernoulli`
Beta `beta`	`RiskBeta` `RiskBetaGeneral` `RiskBetaSubj`^†
Binomial `binom`	`RiskBinomial`
Burr III (Dagum) `burr`	`RiskDagum`
Burr XII `burr12`	`RiskBurr12`
Cauchy `cauchy`	`RiskCauchy` Percentiles: `RiskCauchyAlt` `RiskCauchyAltD`
Chi-squared `chi2`	`RiskChiSq` Percentiles: `RiskChiSqAlt` `RiskChiSqAltD`
Compound (frequency × severity) `compound`	`RiskCompound`
Cumulative `cumul`	`RiskCumul` `RiskCumulD`^†
Discrete `custom`	`RiskDiscrete` `RiskDUniform`
Exponential `expon`	`RiskExpon` Percentiles: `RiskExponAlt` `RiskExponAltD`
Extreme value (max, Gumbel) `gumbel_r`	`RiskExtValue` Percentiles: `RiskExtValueAlt` `RiskExtValueAltD`
Extreme value (min) `gumbel_l`	`RiskExtValueMin` Percentiles: `RiskExtValueMinAlt` `RiskExtValueMinAltD`
F `f`	`RiskF`
Fatigue life (Birnbaum–Saunders) `fatiguelife`	`RiskFatigueLife` Percentiles: `RiskFatigueLifeAlt` `RiskFatigueLifeAltD`
Fréchet `invweibull`	`RiskFrechet` Percentiles: `RiskFrechetAlt` `RiskFrechetAltD`
Gamma, Erlang `gamma`	`RiskGamma` `RiskErlang` Percentiles: `RiskGammaAlt` `RiskGammaAltD`
General (relative weights) `general`	`RiskGeneral`
Histogram `histogram`	`RiskHistogrm`
Hyperbolic secant `hypsecant`	`RiskHypSecant` Percentiles: `RiskHypSecantAlt` `RiskHypSecantAltD`
Hypergeometric `hypergeom`	`RiskHypergeo`
Integer uniform `randint`	`RiskIntUniform`
Inverse Gaussian `invgauss`	`RiskInvgauss` Percentiles: `RiskInvgaussAlt` `RiskInvgaussAltD`
Johnson SB `johnsonsb`	`RiskJohnsonSB`
Johnson SU `johnsonsu`	`RiskJohnsonSU`
Kumaraswamy `kumaraswamy`	`RiskKumaraswamy`
Laplace `laplace`	`RiskLaplace` Percentiles: `RiskLaplaceAlt` `RiskLaplaceAltD`
Lévy `levy`	`RiskLevy` Percentiles: `RiskLevyAlt` `RiskLevyAltD`
Log-logistic `fisk`	`RiskLogLogistic` Percentiles: `RiskLogLogisticAlt` `RiskLogLogisticAltD`
Logistic `logistic`	`RiskLogistic` Percentiles: `RiskLogisticAlt` `RiskLogisticAltD`
Lognormal `lognorm`	`RiskLognorm` `RiskLognorm2` Percentiles: `RiskLognormAlt` `RiskLognormAltD`
Negative binomial, geometric `nbinom`	`RiskGeomet` `RiskNegbin`
Normal `norm`	`RiskNormal` `RiskErf`^† Percentiles: `RiskNormalAlt` `RiskNormalAltD`
Pareto `pareto`	`RiskPareto` Percentiles: `RiskParetoAlt` `RiskParetoAltD`
Pareto II (Lomax) `lomax`	`RiskPareto2` Percentiles: `RiskPareto2Alt` `RiskPareto2AltD`
Pearson V (inverse gamma) `invgamma`	`RiskPearson5` Percentiles: `RiskPearson5Alt` `RiskPearson5AltD`
Pearson VI (beta prime) `betaprime`	`RiskPearson6`
PERT `pert`	`RiskPert`
Poisson `poiss`	`RiskPoisson`
Rayleigh `rayleigh`	`RiskRayleigh` Percentiles: `RiskRayleighAlt` `RiskRayleighAltD`
Reciprocal (log-uniform) `loguniform`	`RiskReciprocal`
Student’s t `t`	`RiskStudent` Percentiles: `RiskStudentAlt` `RiskStudentAltD`
Triangular `triang`	`RiskTriang`
Triangular from percentiles `trigen`	`RiskTrigen` Percentiles: `RiskTriangAlt`
Uniform `unif`	`RiskUniform` Percentiles: `RiskUniformAlt` `RiskUniformAltD`
Weibull `weibull_min`	`RiskWeibull` Percentiles: `RiskWeibullAlt` `RiskWeibullAltD`

A distribution can stand alone or carry one positive multiplier and at most one added or subtracted offset, as in RiskNormal(B1*1.1,B2)*C1+5; its arguments can use numbers, single-cell references and arithmetic, and stay linked to those cells. The property functions and markers:

@RISK property functions, markers and statistics the importer reads
Function	Becomes in xellstorm
`RiskTruncate`	Truncation: truncate_min, truncate_max (before any shift)
`RiskTruncate2`	Truncation: truncate_min, truncate_max of the shifted values (moved back by the shift)
`RiskTruncateP`	Truncation: truncate_pmin, truncate_pmax (percentiles of the distribution)
`RiskShift`	Shift: shift
`RiskName`	Name: the input's name
`RiskLock`	Lock: a fixed value (RiskLock(v), or the RiskStatic value)
`RiskCorrmat`	Correlation: rank correlations between the inputs of one matrix
`RiskDepC`	Correlation: a rank correlation with the input of the same pair name
`RiskIndepC`	Correlation: a rank correlation with the input of the same pair name
`RiskSimtable`	One value per simulation: a fixed cell in the base run, one scenario per further simulation
`RiskOutput`	Output: an output, with the name it gives

What does not convert from @RISK

Functions with no exact equivalent. @RISK’s time-series functions, such as RiskAR1, and RiskPertAlt with the other two-shape percentile forms. For a PERT, give its min, most likely and max, or the percentiles to RiskTrigen, which converts; time series can be set up in xellstorm itself (random walk, AR(1), geometric Brownian motion, mean reversion, jump diffusion).
Formulas the import cannot rewrite. Several distributions in one cell, a distribution inside another function or in a denominator, and arithmetic that would have to be reordered, such as (RiskNormal(0,1)+5)*2. Split them into cells, one distribution each.
Some compound distributions. RiskCompound converts, but not with a deductible, a severity that can be negative (unless it is truncated at 0) or a severity in another cell.
Seeds and statistics. RiskSeed’s stream settings are not kept: xellstorm’s own seed decides the draws. RiskMean and the other functions that report results back into a cell have no value outside @RISK; the same statistics are in xellstorm’s results.
The workbook around the model. VBA macros, user-defined functions and links to other workbooks, as in any workbook xellstorm opens.

Each formula that does not convert is listed with its reason, and the compatibility check names every cell the engine cannot calculate, before you run. Moving a model from an add-in goes through a whole example, with what to do about each formula left.

Moving an @RISK model, step by step

Open the workbook. Drop the .xlsx or .xlsm file into xellstorm; save an .xlsb workbook as .xlsx first. It is read and calculated in your browser tab.
Import the @RISK functions. Import from workbook on the Distributions step lists what becomes an input, an output, a correlation or a scenario, and every formula left, with the reason.
Check what is left. The compatibility check compares the formulas with the values Excel saved and names any cell the engine cannot calculate. Replace those before you rely on the results.
Run and compare. Once everything converts and the check is clean, means and percentiles differ from @RISK’s only by sampling noise. Save the setup as a project file next to the workbook to rerun it later.

Questions

Do I need @RISK or Excel installed?

Neither. xellstorm reads the formulas from the workbook file itself and calculates the model with its own engine in your browser, on Windows, macOS or Linux.

Can I run an @RISK model on a Mac?

@RISK itself runs in Excel for Windows, so on a Mac it needs Windows. xellstorm runs in the browser on macOS as well, and opens the workbook built for @RISK without Excel or the add-in; Chrome and Edge are recommended.

Will I get the same results as @RISK?

The same model, not the same random numbers. Converted distributions keep their parameters and correlations keep their rank correlations. Once everything converts and the compatibility check is clean, means and percentiles differ from @RISK’s by sampling noise, which shrinks as you run more trials; with correlated inputs, each tool pairs the draws its own way, so the tails can differ a little more.

Can I keep using @RISK on the same workbook?

Yes. The import turns the formulas into inputs of xellstorm’s own setup and writes nothing into the file, so the workbook still opens and runs in @RISK.

@RISK is a trademark of its owner. xellstorm is not affiliated with it; its function names appear here only to say what xellstorm reads.

xellstorm is a browser-based Monte Carlo simulation tool for Excel models: no add-in, and the workbook never leaves your computer.

An @RISK alternative that opens your @RISK workbooks

@RISK and xellstorm side by side

Which @RISK functions convert

What does not convert from @RISK

Moving an @RISK model, step by step

Questions

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