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Spreadsheet Sim overview

Spreadsheet Sim lets you run Monte Carlo simulations on existing Excel workbooks without rewriting your model.

What it does​

You upload an .xlsx file, view it in the browser using IronCalc, mark uncertain cells as assumptions (assigning each a probability distribution), mark result cells as outputs, then run N simulation iterations. Each iteration samples new values for every assumption, recalculates the workbook, and records the output values. Results are visualized as histograms, one per output.

Who it's for​

Anyone with a business model, financial projection, or engineering estimate in Excel who wants to understand the range of possible outcomes — not just a single point estimate.

note

Spreadsheet Sim requires a Pro plan. Free users see an upgrade prompt.

Quick start​

Get your first simulation running in a few minutes:

  1. Upload your workbook — Drag and drop an .xlsx file onto the upload area or click to browse. Your workbook opens in the browser with interactive cell selection.
  2. Mark an assumption — Click a cell that represents an uncertain input (e.g., a growth rate or cost estimate) and assign it a probability distribution. You'll see the cell highlighted in blue.
  3. Mark an output — Click a cell whose result you want to track (e.g., net profit or total cost). Output cells are highlighted in green.
  4. Run the simulation — Choose the number of iterations (1,000 is a good starting point) and click Run. The simulation samples new values for every assumption, recalculates the workbook, and records each output — all server-side.
  5. View your results — After the run completes, a histogram appears for each output. Drag the Pr(x < X) line to ask questions like "What's the probability that profit is under $50,000?"
tip

Start with a simple workbook — one assumption and one output — to verify your model behaves as expected before adding complexity.

Key concepts​

ConceptDescription
AssumptionAn uncertain input cell. Each simulation iteration, this cell is overwritten with a value sampled from its distribution.
OutputA result cell or range. Its value is recorded after each iteration.
Iteration (rep)One complete recalculation of the workbook with sampled assumption values.
ConfigA saved set of assumptions and outputs for a workbook, so you don't have to re-configure each session.

Next steps​