Minimum Alternate Tax: companies must pay tax based on book profits when normal tax is lower, with surcharge rules. Minimum Alternate Tax under Section 115JB(1) deems a company's book profits to be its total income where tax under normal provisions is lower than the MAT computation; the tax payable is the higher of tax under normal provisions and tax at the MAT rate on book profits, with prescribed surcharge rules and a concessional rate for qualifying IFSC units.