Advance tax computation: unwithheld or uncollected TDS/TCS cannot be used to reduce advance tax liability. For computing advance tax under clauses (a), (b) or (c) of section 209(1), the tax calculated shall not be reduced by amounts of tax that would be deductible or collectible at source if the person required to deduct or collect has paid or credited the income without deduction or received or debited the income without collection, thereby preventing reliance on unwithheld or uncollected TDS/TCS as offsets against advance tax.