Check your tax return documents, such as your income tax return, assessment notice, or tax correspondence
Look at your tax identification card, if your country issues one
Visit your country’s official tax authority website and use its TIN lookup or verification service
Log in to your online tax account or taxpayer portal
Contact your local tax office or revenue authority directly
Check payroll, employer, or banking records if they were required to collect your TIN
Review business registration documents if the TIN is for a company or sole proprietorship
Ask your accountant, tax preparer, or employer for the number if they previously filed it for you