Semivolatile organic compounds (SVOCs) in indoor environments can partition into the gas phase, airborne particles, and settled dust and onto available surfaces. A long-term dynamic model was developed to predict the hourly concentrations of SVOCs over a year in the gas phase, airborne particles, and settled dust and on each sink surface. The model takes into account mass transfer mechanisms, the reactivity of SVOCs with oxidants indoors, and the influence of four indoor environmental factors (the air temperature, relative humidity, concentration of indoor airborne particles, and air exchange rate) on the mass transfer parameters. The model was validated for DEHP (di-2-ethylhexyl phthalate) and BBzP (butyl benzyl phthalate) by comparing the predicted concentrations in all the phases with the measured concentrations obtained in an environmental chamber and a test house. The model was then used to predict the hourly averaged concentration of BBzP in all the phases under real environmental conditions over a year. More than 52% of the variance in the BBzP concentration was found to be associated with the covariance of the environmental factors. The air exchange rate contributed to 16% of the variance in the concentration. In addition, the indoor air temperature and relative humidity contributed 9% of the variance in the gas-phase concentration of BBzP and 7% of the variance in the settled dust concentration of BBzP. The variance in the concentration of the total suspended particles contributed 10% of the variance in the BBzP concentration on the walls and windows.