Check your tax documents, such as prior tax returns, IRS notices, or tax registration papers
Look for your Social Security Number if you are an individual taxpayer in the United States
Check your Employer Identification Number if you are a business
Review official letters or certificates from your tax authority
Log in to your online tax account or government tax portal
Contact your local tax office or revenue authority
Ask your employer, accountant, or tax preparer
Search your records for tax ID cards, registration forms, or business licenses
Use the tax authority’s official helpline or support service
Visit the official website of your country’s tax authority for TIN lookup guidance