The paper presents a method for generating three-dimensional, time-dependent turbulent inflow data for simulations of spatially developing boundary layers. The approach involves extracting instantaneous velocity planes from an auxiliary simulation of a zero-pressure gradient boundary layer, where the velocity field at a downstream station is rescaled and reintroduced at the inlet. This method, a variant of the Spalart method, is optimized to be implemented in existing inflow-outflow codes with minimal changes. The proposed method produces realistic turbulent boundary layers with statistics that align well with experimental data and direct simulations. It is applied to a large eddy simulation (LES) of a spatially evolving boundary layer over a momentum thickness Reynolds number range of 1530-2150, demonstrating high accuracy and minimal transient near the inlet, which is crucial for minimizing the adverse effects of inflow errors. The method is also extended to non-zero pressure gradients, further enhancing its applicability.The paper presents a method for generating three-dimensional, time-dependent turbulent inflow data for simulations of spatially developing boundary layers. The approach involves extracting instantaneous velocity planes from an auxiliary simulation of a zero-pressure gradient boundary layer, where the velocity field at a downstream station is rescaled and reintroduced at the inlet. This method, a variant of the Spalart method, is optimized to be implemented in existing inflow-outflow codes with minimal changes. The proposed method produces realistic turbulent boundary layers with statistics that align well with experimental data and direct simulations. It is applied to a large eddy simulation (LES) of a spatially evolving boundary layer over a momentum thickness Reynolds number range of 1530-2150, demonstrating high accuracy and minimal transient near the inlet, which is crucial for minimizing the adverse effects of inflow errors. The method is also extended to non-zero pressure gradients, further enhancing its applicability.