Responsible Additions and Increases to Sustain Employee Health Benefits Act of 2018 This bill amends the Internal Revenue Code to allow unused health flexible spending arrangement (FSA) account balances (or a portion of the balances) to be carried forward into the next plan year. For a year in which a balance is carried forward from the preceding year, the dollar limitation on salary reduction contributions to an FSA must be reduced by the amount by which the carried forward balance exceeds $500.