Sample Size and Power Calculation for Two Co-Primary Endpoints R package twoCoprimary version 1.0.0 Comprehensive functions to calculate sample size and power for clinical trials with two co-primary endpoints. The package supports five endpoint combinations: two continuous endpoints (Sozu et al. 2011 <doi:10.1080/10543406.2011.551329>), two binary endpoints using asymptotic methods (Sozu et al. 2010 <doi:10.1002/sim.3972>) and exact methods (Homma and Yoshida 2025 <doi:10.1177/09622802251368697>), mixed continuous and binary endpoints (Sozu et al. 2012 <doi:10.1002/bimj.201100221>), and mixed count and continuous endpoints (Homma and Yoshida 2024 <doi:10.1002/pst.2337>). All methods appropriately account for correlation between endpoints and provide both sample size and power calculation capabilities. Software Depends: R (>= 3.5.0) Imports: mvtnorm, pbivnorm, fpCompare, stats Suggests: dplyr, knitr, rmarkdown, testthat (>= 3.0.0), tibble, tidyr, readr Gosuke Homma <my.name.is.gosuke@gmail.com> Comprehensive R Archive Network (CRAN) Gosuke Homma [aut, cre] (ORCID: <https://orcid.org/0000-0002-6854-5627>) MIT + file LICENSE (https://CRAN.R-project.org/package=twoCoprimary/LICENSE) 2025-11-21 application/tgz https://CRAN.R-project.org/package=twoCoprimary doi:10.32614/CRAN.package.twoCoprimary en-US