Capitalizing on the existing crystalline silicon industry, double-side textured perovskite-silicon tandem solar cells have a huge potential to penetrate the electricity market. To systematically enhance their performance, a comprehensive understanding of loss mechanisms in the device is needed. Herein, we combine various characterization methods, namely spectrally resolved photoluminescence (PL), transient-PL, PL-based implied open-circuit voltage imaging, spectrometric characterization, and Suns-Voc measurements to quantify current density–voltage (jV) photovoltaic metric losses of a fully-textured perovskite silicon tandem solar cell (26.7% efficiency). The extracted device characteristic parameters are then used as a reference for the comprehensive opto-electrical simulation model (Sentaurus TCAD) which precisely reproduces the experimentally obtained optical and electrical solar cell characteristics. Subsequently, starting from the current device design, we alleviate one step at a time the loss constrains and show the impact of each loss channel on the efficiency, identifying the three major ones to be at the (i) perovskite/C60 interface, (ii) the series resistance, and (iii) parasitic absorption, which limit the Voc, FF, and Jsc of the device, respectively. Furthermore, we demonstrate that a practical efficiency potential of 39.5% can be regarded as practical limit for the presented tandem device architecture. This work emphasizes the importance of loss analysis studies and provides guidelines for future solar cell design optimizations.