As the April 15 deadline for filing 2018 U.S. personal income tax returns approaches, some taxpayers will find themselves short of the amount they need to pay their tax bill. Miron Lulic, founder and CEO of SuperMoney, an platform for evaluating financial services products, notes that the consequences of not filing a return or not paying taxes include missing out on a refund, or incurring interest charges, penalties and levies. Whether the problem is a short-term cash flow constraint or an unexpected tax liability, Mr. Lulic has a few tips on how to handle the situation.