@RISK: Speed Up Performance

Speed up @RISK: clear sim results data, use 64-bit Excel, enable multi-threaded calculations, add RAM, structure models efficiently, minimize open workbooks, and optimize sim settings.

Dec 18, 2025
Knowledge

Title

Answer

How to Speed Up @RISK Performance

Applies to: @RISK 5.x and Up

Contents:

Clearing @RISK Simulation Results Data
Excel settings
Hardware
Windows Settings
@RISK model structure
Simulation settings
Progress Window
@RISK with projects
Project settings

Background:

When @RISK saves simulation results into the workbook, the workbook file size grows. This can eventually impact performance.

@RISK performance can also be influenced by Excel setup, computer hardware, Windows settings, model structure, simulation settings, and use with Microsoft Project.

The tips below include measures within @RISK and external optimizations. Bolded items tend to have the biggest impact.

Clearing Simulation Results Data

To clear them:

Go to Utilities → Clear @RISK Data → Simulation Results → OK, then save the workbook OR
Export results first via Utilities → Save Simulation File.

To prevent future file bloat, change Utilities → Application Settings → Save Results from Automatically Save in Workbook to Prompt on Save, Save to External File, or Never Save Results.

Save to External File: @RISK prompts to save results to an .RSK5 file when you save the workbook.
Prompt on Save: Prompts each time; default is workbook unless you change it.
Never Save Results: Results aren’t stored automatically; you can still export with Utilities → Save Simulation File.

To reopen saved results later, open the model first.

If @RISK doesn’t find the .RSK5 file, use Utilities → Open Simulation File. Large files may require 64-bit Excel.

1. Excel Setup

Switch to 64-bit Excel for large simulations to overcome 2 GB memory limits in 32-bit Excel. Requires @RISK 5.7+ for 64-bit.
Enable multi-threaded calculations:
- Excel 2010+: File → Options → Advanced → Formulas → Enable multi-threaded calculations
- Excel 2007: Office Button → Excel Options → Advanced → Formulas → Enable multi-threaded calculations
Install Excel locally if running from a network to avoid slowdown from network traffic.
Remove unnecessary add-ins:
- Excel 2010+: File → Options → Add-Ins → Manage → Excel/COM → Go → uncheck unneeded add-ins
Keep Excel updated: Install latest service packs or upgrade to Office 2010+.
Follow best practices in Lumivero/Microsoft guides for Excel performance.

2. Hardware

Add RAM: Insufficient memory is often the biggest bottleneck. Monitor hard-drive activity during simulations to assess needs.
Enable Turbo Boost / Turbo Core / Power Tune if available on your CPU.

3. Windows Settings

Increase page file size for large simulations.
Ensure %TEMP% folder is local, clean, and has ample space.
Maintain plenty of free disk space.
Close other applications and background services.
Configure antivirus to exclude .XLS/.XLSX files (with caution).

4. Model Structure

Structure your model efficiently; poorly structured models slow simulations.
Embed severity distributions in RiskCompound() rather than using cell references.
Fix invalid correlation matrices to prevent repeated pop-ups and recalculations.
Remove unnecessary graphs, tables, external links, and linked pictures.
Move @RISK functions out of Excel tables.
Replace slow formulas (INDIRECT, VLOOKUP, HLOOKUP) with faster alternatives (e.g., INDEX+MATCH).
Avoid saving simulation results in the workbook during simulation.
Open only the workbooks required for the simulation.

5. @RISK Simulation Settings

Multiple CPU Support: Set to Automatic or Enabled for multi-core processors.
View tab: Deselect Demo Mode, Update Windows During Simulation, Show Excel Recalculations.
Sampling tab:
- Use Latin Hypercube for most simulations.
- Set Collect Distribution Samples to None or Inputs Marked with Collect.
- Disable Smart Sensitivity Analysis to speed up simulation start.
- Update statistic functions At the End of Each Simulation for faster processing of many stats.
Convergence testing: Enable to avoid unnecessary extra iterations; adjust iteration limits as needed.
Monitor progress window: If iterations/sec drops, give Excel focus to restore speed.

6. Using @RISK with Microsoft Project

Upgrade to the latest @RISK version for faster project simulations.
Use the accelerated engine where possible; check model compatibility via Check Engine.
Turn off Demo Mode and Show Excel Recalculations if using the standard engine.
Prefer risk registers over probabilistic branching.
Upgrade to Project 2010+ for faster recalculations (Project 2003 is fastest for @RISK 6.x).
In Project settings:
- Uncheck unnecessary statistics options (Critical Indices, Probabilistic Gantt Chart, Timescaled Data).
- Set simulation Date Range to only future activities.
- Avoid re-importing .MPP files; keep the linked Excel workbook.

7. Microsoft Project Recommendations

Copy project to a local drive (SSD preferred).
Zero out margin spans, set future constraints to ASAP, remove deadlines.
Check for negative slack and unstatused tasks.
Create a table with only fields needed for @RISK prior to import.

Summary:
Improving @RISK performance involves optimizing Excel and hardware, structuring your model efficiently, adjusting simulation settings, and applying best practices when using Microsoft Project. The most impactful improvements are using 64-bit Excel, enabling multi-threaded calculations, adding RAM, and structuring models efficiently.

Related Articles:

Excel:

Repair of Excel or Project

Getting Better Performance from Excel

Excel Tables and @RISK

Switch to 64-bit Excel

CPUs/Memory:

Out of Memory

Memory Used by @RISK Simulations

Virtual Memory Setting

CPUs Used by @RISK 7.x

Temp Folder: