You have a Microsoft 365 subscription and Microsoft 365 E5 licenses assigned to your users. You are planning the deployment of Microsoft Defender for Identity to protect your on-premise Active Directory users, and need to determine the capacity for your deployment. What should you use?

Answer options:

A.The Defender for Identity Sizing Tool
B.The Total Cost of Ownership (TCO) calculator
C.Azure Migrate
D.The IdFix tool

Correct Answer: A 
You should download and run the Defender for Identity Sizing Tool, which will generate an Excel file with detailed information about the capacity requirements.
The Sizing Tool is found here: Option B is incorrect. The TCO tool is used to calculate the savings achieved by moving workloads to Azure.
Option C is incorrect. Azure Migrate is used to facilitate migration of workloads to Azure.
Option D is incorrect. The IdFix tool is used to fix Azure AD user account issues that might cause problems when synchronizing to Office 365.
References: 
To know more about Microsoft Endpoint for Identity capacity planning, please refer to the link below: 

https://docs.microsoft.com/en-us/defender-for-identity/capacity-planning
https://github.com/microsoft/ATA-AATP-Sizing-Tool