A forward, numerical model of the carbonate platform and basin depositional system aids in understanding the roles played by different variables in controlling the growth patterns of carbonate platforms, and thus their internal facies architecture. The numerical model simulates the two-dimensional development of a carbonate platform and adjacent basin by successively calculating and depositing discrete sediment budgets generated over short time periods (104 yr), and displaying the results in synthetic cross sections through the carbonate buildup. A series of model experiments shows that the effect of changing the eustatic sea level is largely dependent on the rate of subsidence. In general, sea-level fluctuations tend to restrict progradation of the platform by producing periods of exposure of the platform top that decrease the overall sediment budget available for deposition on the marginal slope. Either increasing the amplitude or decreasing the period of the sea-level cycle also restricts progradation, which suggests that the higher order (short period) sea-level cycles that are evident in the rock record may play an important role in controlling the cross-sectional geometry of carbonate platforms. Forward models such as the one presented here may provide a basis for creating an inverse model that could be used to closely constrain the variables such as sediment production rate, subsidence, and sea-level history that led to the cross-sectional geometry observed in the field or in a seismic section.