Truncation Time Selection for Average Hazard Analyses R package AHTauDesign version 0.1.0 Implements a two-stage, design-informed framework for selecting the truncation time in time-to-event trials analyzed with the average hazard estimand, motivated by pediatric oncology settings with small samples, slow accrual, and limited follow-up. Stage 1 validates a clinically proposed truncation time against the planned design using simulation-based diagnostics for risk-set support, follow-up coverage, estimability, and estimator stability, classifying it as Pass, Borderline, or Fail. Stage 2 performs constrained optimization over a grid of candidate truncation times within a clinical-distance window, maximizing a utility subject to feasibility constraints, with an independent evaluation run to assess the selected time. Supports proportional-hazards, early-, and delayed-effect patterns, uniform accrual with administrative censoring, and calibrated exponential random censoring. Software Depends: R (>= 4.1.0) Imports: survival, stats, utils Suggests: ggplot2, knitr, rmarkdown Xinyue Zhao <xinyuezhao27@gwu.edu> Comprehensive R Archive Network (CRAN) Xinyue Zhao [aut, cre], Haitao Pan [aut] GPL-3 2026-09-10 application/tgz https://CRAN.R-project.org/package=AHTauDesign doi:10.32614/CRAN.package.AHTauDesign