Suction caissons are promising foundations for offshore wind turbines, but their serviceability performance under long-term cyclic lateral loading remains difficult to assess. This study develops a three-dimensional finite element framework to investigate the monotonic and cyclic response of suction caissons in sand, with particular focus on accumulated tilt. The model combines hypoplasticity with intergranular strain for the monotonic and early cyclic response with the High-Cycle Accumulation model for long-term deformation buildup. After validation against field test data under monotonic combined loading, the framework is used in a parametric study to examine the influence of load eccentricity, vertical load, aspect ratio, cyclic loading amplitude, loading symmetry and soil density. The results show that loading symmetry strongly controls tilt accumulation, with maximum normalised rotation occurring under asymmetric two-way loading. Symmetric two-way loading may induce back-rotation, while cyclic shearing produces stress redistribution around the caisson. The numerical trends agree qualitatively and reasonably quantitatively with available experimental evidence. Finally, simplified relationships are calibrated from the finite element results to support preliminary serviceability-oriented design of suction caisson foundations.