Abstract: The need for accurate and reliable information about income and resources available to individuals with psychiatric disabilities is critical for the assessment of need and evaluation of programs designed to alleviate financial hardship or affect finance allocation. Measurement of finances is ubiquitous in studies of economics, poverty, and social services. However, evidence has demonstrated that these measures often contain error. We compare the 1-week test-retest reliability of income and finance data from 24 adult psychiatric outpatients using assessment-as-usual (AAU) and a new instrument, the Timeline Historical Review of Income and Financial Transactions (THRIFT). Reliability estimates obtained with the THRIFT for Income (0.77), Expenses (0.91), and Debt (0.99) domains were significantly better than those obtained with AAU. Reliability estimates for Balance did not differ. THRIFT reduced measurement error and provided more reliable information than AAU for assessment of personal finances in psychiatric patients receiving Social Security benefits. The instrument also may be useful with other low-income groups.