TAN is an alphanumeric 10 digit number required by a person who is liable to deduct TDS and file TDS return. Thus such a person must make an application within a month in which TDS was deducted for allotment of Tax Deduction and Collection Number (TAN) in form 49B. This number allotted is mandatory to mention in all TDS Certificates issued, returns, challans, etc. If a person fails to apply for TAN he may be penalized up to Rs. 10,000/-.