Gather all missing tax documents for each year you need to file
Download the correct tax forms and instructions for each specific tax year
Use tax software, a tax professional, or paper forms that match each year
Complete one separate return for each unfiled tax year
Check whether you are due a refund or owe taxes for each year
File the oldest unfiled return first if required by your tax authority
Sign and date each return before submitting
Mail paper returns to the correct address for that tax year if e-filing is unavailable
Keep copies of every return, form, and supporting document
Pay any taxes, penalties, or interest owed as soon as possible
Contact the tax authority if you need help with prior-year filing rules
File as soon as possible to avoid losing refunds or increasing penalties