A Complex Installment Agreement is a payment plan for taxpayers who owe over $50,000. The balance must be paid off within five years (60 months) or before the Collection Statue Expiration Date. Interests and penalties may still be issued by the IRS until the full amount is paid. Financial information must be provided in order to determine a minimum monthly payment.. The monthly payment will be determined by subtracting the taxpayers allowable monthly expenses from him monthly gross income. A tax attorney can negotiate this monthly payment to as little as possible. Consult a tax attorney to determine if a Complex Installment Agreement is the best solution for your debt situation.