If you choose not to upgrade your account to one of the paid plans, it will automatically transition to the Free plan (5 collaborators and 5 private projects). If your usage exceeds the limits of the Free plan, your projects will become read-only until you either (1) upgrade to a plan that supports your level of use, or (2) lower the number of active private projects and/or collaborators.
You’ll get reminders before your trial ends, but you can disregard them if you are using Tracker within the Free plan limits. You can also visit your Plans & Billing page (click Accounts under your username, at the top right of Tracker, then Manage Account) to view your trial end date (as outlined in the image above).
You can choose a paid plan and enter billing information before your Free Trial ends; however, you will not be charged (or receive a receipt) until the trial has concluded. In this case, you can view your first payment date in the Payment History section of your Plans & Billing page (click Accounts under your username, at the top right of Tracker, then Manage Account).