To claim a refund, you must file an amended return within 3 years after the date you filed your original return or 2 years after the date you paid the tax. Many find the easiest way to figure the entries for Form.X is to first make the changes in the margin of the return they are amending. Find Quarterly Sales Tax filer forms and instructions. You can deduct a part of your medical and dental expenses, and amounts you paid for certain taxes, interest, contributions, and other expenses. You can amend your return at any time, but to claim a refund, the amended return must be filed within three years from the original due date of the return.