In recent years, hydraulic fracturing design has evolved significantly. Fluid volumes injected in a lateral have more than doubled to ~ 250,000 bbl/well ( Weijers et al., 2019 ). Increased injection volumes coupled with a sub-optimal completion design can lead to over-stimulation at current well spacing densities. In many instances, dominant clusters that take a majority of the injected fluid during child well treatment intersect offset parent wells. This results in sub-optimal reservoir drainage, highly inefficient fluid and sand placement and negatively impacts the overall well productivity due to well interference. In this work, we analyze offset well pressure measurements in the Permian Basin to evaluate if a frac job is overstimulated. Additionally, we perform numerical modeling studies to evaluate the extent of overstimulation in different stimulation scenarios and provide recommendations to maximize the capital efficiency of a frac job. We analyze the pressure response in offset parent wells in the Permian Basin during treatment of a nearby well. Fracture arrival times (time taken for the child well fractures to intersect with a nearby parent well) are investigated for multiple stages during child well stimulation. This information from field data is coupled with fracture modeling simulations to evaluate if a frac-job is over-stimulated. Stages that suggest over-stimulation are systematically analyzed and dynamic plots are presented, that compare the capital efficiency at different times during a frac job. Optimal completion designs that achieve uniform distribution of injected fluid volumes into multiple clusters are key to successful fracturing jobs. Simulations as well as field data show that if a large job volume is pumped with a sub-optimal completion design, fracture arrival at the offset well is early, leading to over-stimulation and wasted capital. In such a scenario, dominant clusters that take most of the injected fluid can intersect nearby offset well early in the treatment, while significantly bypassing undepleted reservoir rock along the lateral (that should ideally be drained) due to low cluster efficiency. This results in a frac job with poor capital efficiency and a well with lower productivity (due to interference with offset well). We show that early fracture arrival times are indicative of fewer clusters propagating fractures with very non-uniform fluid distribution (low cluster efficiency), whereas late arrival times indicate more uniform fluid distribution in the clusters with high cluster efficiency. We introduce a novel technique that analyzes field offset well pressure data and fracture arrival times at the offset well to diagnose stimulation efficiency and prevent over-stimulation. Our method provides operators with a relatively inexpensive way to improve capital efficiency during a frac-job.