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. Get Paid for Going Green Those looking into environmentally minded home modifications may get a boost from Uncle Sam’s tax incentives. Tax Freedom Day Assess how many days you'll work to pay your federal tax liability.