The percentage of your pretax pay that you contribute into a retirement account, such as a 401(k) or 403(b). While making pretax retirement plan contributions does lower your take-home pay, it also lowers your current federal income taxes. The amount you contribute toward your retirement plan will be greater than the reduction in your paycheck. The maximum salary deferral contribution to a 401(k) or 403(b) plan in 2018 is $18,500, or $24,500 for individuals age 50 and older. This calculator allows you to deduct up to 80% of your pay, but you should check with your plan sponsor about your plan’s provisions.