Understanding and quantifying charge collection at interfaces is essential for optimizing solar cell performance, particularly as interfacial losses increasingly limit device efficiency. Despite their importance, interfacial collection efficiencies are difficult to estimate directly from standard measurements. Here, a novel analytical method is presented to calculate optoelectronic parameters based on the internal quantum efficiency (IQE) at the weak and strong absorption regimes. This approach allows to determine meaningful physical parameters such as the average and front-surface collection efficiencies, revealing imperfect carrier collection in perovskite solar cells. By applying the method to devices with and without an electron transport layer, clear differences in interfacial extraction efficiency are revealed, showcasing the method's utility. The results suggest that the total collection cannot be described by simple multiplicative or additive electron and hole collection models, but rather reflects a more nuanced interplay governed by extraction velocities. The proposed methodology offers rapid evaluation of device interfaces without relying on transient techniques or traditional IQE models in which perfect carrier extraction is assumed.