If you invoice your clients for work time, you can use the Billable option that can be associated with a time record. Records marked as billable will get into invoices. You can also filter reports depending on the status of this flag. The Billable option on time entry page of Time Tracker
How to Enable the Billable Checkbox
To see the Billable checkbox in Time Tracker enable the Invoices plugin for your group. You can do it on the Plugins page. The Invoices plugin depends on the Clients plugin to be enabled, so enable them both. Enabling the Invoices plugin Time Tracker FAQ
