Tax Extension Act of 1991

Tax Extension Act of 1991 - Title I: 6-Month Extension of Certain Expiring Tax Provisions - Amends the Internal Revenue Code to extend for six months the following expiring provisions: (1) the rules on allocating research and experimental expenditures in determining income from sources within or without the United States; (2) the credit for increasing research activities; (3) the tax exclusion for employer-provided educational assistance; (4) the tax exclusion for employer-provided group legal services plans; (5) the targeted jobs credit; (6) the energy investment credit for solar and geothermal property; (7) the low-income housing credit; (8) the authority to issue mortgage revenue bonds and mortgage credit certificates; (9) the authority to issue qualified small issue bonds to finance manufacturing facilities and farm property; (10) the itemized deduction for health insurance costs of self-employed individuals; (11) the credit for clinical testing expenses for certain drugs for rare diseases or conditions; and (12) the tax credit for charitable contributions of appreciated tangible property.

Title II: Modification to Corporate Estimated Tax Provisions - Provides for a temporary increase (taxable years beginning after 1991 and before 1997) in the amount of installment payments in the case of corporations that underpay estimated taxes.