The Facts About Income Tax Millions faithfully file their 1040 forms each April. But some things about federal income taxes may surprise you. Related Content Deciding When to Take Social Security One of the most common questions people ask about Social Security is when they should start taking benefits. Insuring Your Business Against Cyber Liability 90% of small businesses in the U.S. don't protect their data from cyber attacks. Is your business at risk? Federal Income Tax Use this calculator to estimate your income tax liability along with average and marginal tax rates.