Accurate estimates of flood inundation areas are essential for effective risk assessment, disaster response, and infrastructure resilience. Flood hydrographs are crucial for predicting flooding extent and impact. This study, conducted in the Klawing watershed in Purbalingga Regency, Central Java, enhances flood risk management by examining the effects of incorporating multiple river subbasins in hydrograph estimation. Using the HEC-HMS model, flood hydrographs based on a 25-year return period of extreme rainfall were simulated from data from seven rainfall stations. Three scenarios were created: 1-basin, 3-subbasins, and 5-subbasins. Results show increased peaks with more subbasins: 1967.8 m3/s for 1 basin, 2001.4 m3/s for 2 subbasins, and 2149.7 m3/s for 5 subbasins, due to the superposition of lag and travel times. The steeper northern subbasins cause more simultaneous rainfall accumulation.