Can I file my 90-day report after the due date and where should I go in Bangkok?

You can file your 90-day report in person starting from two weeks before your due date until seven days after. Filing on Monday, after your due date of Saturday, is permissible without penalty, but a fine of 2000 baht applies from the eighth day after the due date. In Bangkok, you should go to the main immigration office at the Government Complex Building B (South Entrance), Counter A. Alternatively, you can also consider using the online reporting system if you've done it before.