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 Capital Gains Tax Estimator Use this calculator to estimate your capital gains tax. Does Your Child Need to File an Income Tax Return? When your child has income, there’s a good chance that he or she will need to report it and pay taxes. The Rule of 72 Do you know how long it may take for your investments to double in value? The Rule of 72 is a quick way to figure it out.