The paper addresses the problem of reduced load capability of bolted joints in aircraft structures when shims are used. Shims are a common means of compensating assembly gaps; however, their presence introduces additional eccentricities and may lead to inaccurate strength assessment of the joint. Traditionally, the McCombs method is applied to determine the allowable bending loads on fasteners. This method is based on the plastic bending hypothesis and enumerates several calculation cases. At the same time, it has certain limitations: it inadequately describes the stress state in thin members, disregards differences between dry-pin and wet-pin testing, and complicates the selection of the appropriate formula for a specific configuration. This work proposes a modified calculation method, which introduces a new formula for joints with very thin members, a correction factor to account for bearing test conditions, an algorithm for selecting the formula depending on member thickness and bearing depth, as well as a refined strength reduction factor for fasteners that considers countersink geometry and shim thickness. The developed approach avoids incorrect results in boundary cases (very thin or thick members, thin or thick shims, significant differences in the mechanical properties of joint components), thereby improving the accuracy of strength evaluation. The obtained relations and algorithm can be applied in the design and strength analysis of aircraft structures, as well as in the assessment of the impact of deviations, rework and repairs on the load capability of bolted joints.