How the 'Find Duplicates' Button Works on Lead Records in Salesforce Classic

The Find Duplicates feature is only available in Salesforce Classic and performs an OR search across all checked criteria fields using wildcard matching.

The Find Duplicates search does an OR search on all the criteria boxes checked.  Checking more boxes will return more results. 

It does a wild card search on the entire phrase of the checked box, in all the standard search fields of the object (Lead, Contact, Account, Opportunity). It includes columns not shown on the Find Duplicates return screen; such as the website on the Account record. 

Example: *Acme Insurance* will not return companies with just "Acme" in the name. 
If you have: 
Company name Acme Insurance 
Lead first name Bob 
Lead last name -- Wye

It will perform the query as :
(*Acme Insurance*) OR (*Bob* AND *Wye*)

Further details on merging duplicate leads, including the permissions required to use this feature, can be found here: Merge Duplicate Leads.
 

Notes:

• This feature is only available in Salesforce Classic.
• Lightning Experience uses an automated widget that scans for potential duplicates. For steps on how to set it up, see Show Duplicate Records in Lightning Experience.