Introduction: Population aging and increasing long-term care needs call for designing and implementing better tools for assessing functional ability. In Chile, the Lawton and Brody (L&B) scale is used for identifying limitations with instrumental activities. This study compared the costs and acceptability of the L&B with a new instrument to measure instrumental activities of daily living (IADL): the Instrument for the Assessment of Functionality Stages (Instrumento de Evaluacion de Estadios de Funcionalidad; IDEEF). Methods: Phone surveys were carried out to apply the L&B and the IDEEF to a sample of 200 older people (60+) participating in public programs for older people in the Metropolitan Region, Chile. Besides the items assessed by each scale, the survey captured completion times and included a short questionnaire on acceptability, data that allowed comparisons between instruments. Results: On average, the L&B takes around 4 min to be applied; the completion times for the IDEEF are 4 times longer. However, the IDEEF performs better in terms of acceptability and has neither gender bias nor dependency bias. Conclusion: Both instruments have pros and cons, but the IDEEF appears as a feasible alternative to the L&B to improve the assessment of IADL in the country.