CPU spikes when typing in classic Outlook for Windows

Last Updated: May 12, 2025

ISSUE

When you write an email in classic Outlook for Windows, you may notice the CPU spikes up to 30 to 50% at some times and increases the power consumption. You can observe this if Task Manager is open while you type.

This issue can occur after updating to Version 2406 Build 17726.20126+ on Current Channel, Monthly Enterprise Channel, or the Insider channels.

STATUS: FIXED

The Word Team implemented a fix which will go to the following channels soon:

Beta Channel (Version 2505 Build 18822.15000) – ETA April 30, 2025, reference Update History for Office Beta Channel - Office release notes. Current Channel Preview (Version 2505 18827.20008) – ETA May 5, 2025, reference Update History for Office Current Channel (Preview) - Office release notes. Current Channel (Version 2504 18730.20158) – ETA May 13, 2025, reference Update history for Microsoft 365 Apps (listed by date) - Office release notes. Monthly Enterprise Channel (Version 2503 18623.20256) – ETA May 13, 2025, reference Update history for Microsoft 365 Apps (listed by date) - Office release notes. Monthly Enterprise Channel (Version 2502 18526.20332) - ETA May 13, 2025, reference Update history for Microsoft 365 Apps (listed by date) - Office release notes.

To work around the issue, you can switch to Semi Annual Channel which does not have the change that causes the issue.

Use a registry key to switch to Semi Annual Channel. For more information, go to Use a registry command to install Microsoft 365 Insider on Windows device.
1. Open a Command Prompt window with Run as administrator for Administrator context.
2. Paste the command below and press Enter:reg add HKLM\Software\Policies\Microsoft\office\16.0\common\officeupdate /v updatebranch /t REG_SZ /d SemiAnnual
3. After you add the registry key, select File > Office Account > Update Options, then Update Now to initiate the switch to Semi Annual Channel.
Use the Office Deployment Tool to switch to Semi Annual Channel. For more information, go to Change the Microsoft 365 Apps update channel for devices in your organization.

A way to test and confirm the issue is to revert to Version 2405 before the change was introduced. This is not recommended since there have been security updates since that version. To make the change do the following:

Locate the build of Version 2405 for the respective channel you are on from Update history for Microsoft 365 Apps (listed by date).
Open a Command Prompt (Run as Administrator).
Type or past the command below and put the build from Step 1 and then press Enter:"%programfiles%\Common Files\Microsoft Shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.17628.20144

Alternately you can use the Office Deployment Tool to switch to an earlier version of a channel. For more information, go to How to revert to an earlier version of Office.