Natively, Trello offers reporting via Butler—this won't exactly provide a percentage of completion, but it does offer a lot of customization to report on what you want: https://help.trello.com/article/1192-creating-reports-with-butler
Beyond that, I would suggest having a look at these Power-Ups to see if any would meet your needs: https://trello.com/power-ups/category/analytics-reporting
If you had to thrive a new habit during a lockdown, what would it be? Trello
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events