The best way to determine your type is through the administration of a test by a certified type professional, typically coupled with an interview. The price varies from $10 to over $100. There are a number of popular free assessments out there but this is one of those things where you often get what you pay for. You can also start a “Type Me” thread on the site here. However before you do that, it’s recommended that you do a little bit of personal research first. You’ll get much better responses if you’ve narrowed things down a little and ask both thoughtful questions and provide meaningful information. Read some materials on the systems, understand the basics about the different types and take one or two reputable assessments. Don’t be surprised if it takes you a little bit of time to accurately figure out your type (weeks to months) and realize that these assessments are far from perfect.
The following are some threads that can help direct you to some assessments that are the better ones.