The Facts About Income Tax Millions faithfully file their 1040 forms each April. But some things about federal income taxes may surprise you. Share | Related Content Federal Income Tax Use this calculator to estimate your income tax liability along with average and marginal tax rates. “Dirty Dozen” Tax Scams to Watch For Every year the IRS releases its list of tax scams, spotlighting some ways that people try to separate you from your money. Social Security Taxes Estimate how much of your Social Security benefit may be considered taxable.