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, select Settings and proceed to the Options section. 

Once there, under the Transactions section, you can activate "Include Soft Credits in Gift Calculations" and then hit the green Save button at the bottom of the page. The summary giving columns on the Constituents Grid, like YTD Received Amount and Cumulative Received Amount, will then reflect direct transactions plus any soft credits.

Please note these calculations will refresh overnight, so you will need to wait until the next morning to see the changes. If you turn this feature off in the future, it will also need an overnight refresh to reflect the change.