Applies to: @RISK for Excel, all releases

Why doesn’t my @RISK macro run for all iterations?

Issue
You’ve configured @RISK to run a VBA macro at every iteration, and the macro modifies the workbook. However, some changes appear to be missing after the simulation finishes.

Cause
This usually happens when Multiple CPU is set to Enabled in Simulation Settings.

In a multiple-CPU simulation, @RISK runs several parallel copies of Excel:

• One master CPU (with the visible Excel window)

• One or more worker CPUs, each with its own temporary copy of the workbook

The master CPU distributes blocks of iterations to the worker CPUs. Those workers return random numbers for @RISK distributions, but any VBA changes made in their workbook copies are discarded when the simulation ends. Only changes made in the master copy persist.

As a result, your macro is running—but not all workbook changes survive.

Solutions

1. Disable Multiple CPU
   If performance allows, set Multiple CPU = Disabled.
   This ensures there is only one workbook instance, so all VBA changes are retained.

2. Use a VBA User-Defined Function (UDF)
   If you need VBA-generated values during simulation:

   • Convert the macro into a UDF that returns a numeric value

   • Call the UDF from a worksheet formula

   • Make that cell an @RISK output

   To retain iteration-level results:

   • Use RiskData() functions (may slow large simulations), or

   • Generate a Simulation Data report after the simulation (faster for large models)