An experiment that is ‘in progress’ can be marked as ‘complete’, to help your team keep track of the status of your work and will update the completeness tracker on the subproject level as well.

Click on the ‘Complete experiment’ button in the upper right-hand corner of the experiment page:

In addition to the ‘Complete experiment’ button, you can also mark an experiment as complete by selecting ‘Completed’ in the status dropdown which can be found in the expanded experiment header...

…or in the ‘Experiment details’ section of the experiment’s ‘Overview’ tab.