Abstract Ocypode gaudichaudii is widespread on Peruvian sandy beaches, yet information on its population dynamics remains scarce despite its key role in beach ecosystem functioning. We conducted the first year-round assessment of population status and morphometric maturity of O. gaudichaudii on the central coast of Peru (Chancayllo beach). Specifically, we quantified sex ratio, size structure, annual population density, and size at first morphometric maturity (CW 50 ) using the two traits most strongly correlated with carapace width (CW): cephalothorax length (CL) and total chela length (TLC). Across the year, the population showed an annual sex ratio ≈1 : 1, a dominant adult size class of 37.5-42.5 mm CW, and 0.76 ind m −2 average density, with no significant seasonal differences in density. Sexes were analysed separately because ANCOVA detected significant sex effects on slopes and intercepts for both CL and TLC. The two-phase Somerton model provided CW 50 estimates of 19.8 mm (95% CI 17.2-20.6) for females using CL and 18.5 mm (15.6-21.3) using TLC; for males, CW 50 was 18.0 mm (14.9-21.0) with CL and 19.0 mm (16.4-21.7) with TLC, and the two-phase model outperformed a single linear model in all comparisons. Complementary Spline analyses located change-points in relative growth at 12.6 mm (females, CL), 24.2 mm (females, TLC), 16.9 mm (males, CL), and 16.1 mm (males, TLC), reflecting a more gradual transition in growth. Together, Somerton and Spline approaches yielded concordant maturity thresholds (Somerton with narrower uncertainty), providing the first quantitative baseline for monitoring and managing O. gaudichaudii on Peru’s central coast.