Excel slowness is usually one of: massive file size, runaway calculations, an add-in, or a corrupt file.

1. How big is the file?

File size correlates with how Excel feels:

  • Under 5 MB: should be snappy
  • 5-25 MB: noticeable lag during opens and saves
  • 25-100 MB: slow but workable
  • 100+ MB: Excel is the wrong tool — use a database

To check: File Explorer → right-click → Properties.

2. Calculation mode

If Excel pauses for several seconds after every change, automatic recalculation is happening. Switch to manual:

  • Formulas tab → Calculation Options → Manual
  • Press F9 when you want a recalculation

This is essential for files with many complex formulas. Remember to recalc before printing or sharing.

3. Reduce data

The single most effective speedup:

  • Delete unused columns and rows (Ctrl + End shows the "used range" — if it's row 50,000 but you only have data to row 500, there's bloat)
  • Convert formulas to values where possible (Copy → Paste Special → Values)
  • Remove conditional formatting from huge ranges
  • Remove or simplify pivot tables you no longer need

4. Open in Safe Mode

Hold Ctrl while clicking the Excel icon. Skips add-ins and custom settings. If Excel works in Safe Mode but not normally, an add-in is the culprit.

File → Options → Add-ins → Manage → COM Add-ins → uncheck and restart.

5. Big external data

Files that pull from queries (Power Query, ODBC) refresh on open:

  • Data tab → Queries & Connections → review each query
  • Disable auto-refresh on queries you don't need
  • Right-click queries → properties → uncheck "Refresh data when opening the file"

6. Repair the file

If a file crashes Excel every time it opens:

  1. File → Open → browse to the file
  2. Click the down arrow next to the Open button
  3. Choose Open and Repair
  4. Pick Repair

If repair fails, try Extract Data to recover formulas/values into a fresh file.

7. Disable hardware acceleration

Sometimes Excel's GPU rendering causes crashes:

  • File → Options → Advanced → Display
  • Check Disable hardware graphics acceleration

Restart Excel.

8. Update Office

A surprising number of Excel bugs are fixed in updates:

  • File → Office Account → Update Options → Update Now

9. Reduce font and formatting overhead

Beautifully formatted spreadsheets are slow:

  • Excessive borders
  • Many different font sizes
  • Heavy conditional formatting
  • Hundreds of named ranges

Simplifying these often takes a 30 MB file to 5 MB.

10. Power Pivot / data model

If your file has a data model (Power Pivot), the file size includes that — and it loads at open:

  • Power Pivot → Manage → check the size of tables
  • Aggregate or filter to reduce row counts
  • Use measures rather than calculated columns where possible

When to ticket

Open a ticket if:

  • Excel crashes on launch even in Safe Mode
  • A specific file crashes every time and Open-and-Repair fails
  • You need help architecting a different tool (database, dashboard) for a workload that's outgrown spreadsheets

Include the file size, version, and what action triggers the crash.