No, soft credits are not initially included in gift calculations like Last Gift Date, Cumulative Amount Received, etc.

You do have the ability to include soft credits into these calculations as an admin user. To do this you would go to your organization's name, hover over Account in the drop-down and select Settings. Once there, go to the Options tab and you can turn on "Include Soft Credits in Gift Calculations" and then hit the green Save button on the bottom left. 

Please note these calculations will refresh overnight, so you will need to wait a day to see the changes.