This package contains data and scripts to reproduce results of Petrovan, Moor & Schmidt (2025). Trends in abundance change are estimated for Europe’s two most common amphibian species, the common toad (Bufo bufo) and the common frog (Rana temporaria), in Switzerland (1973 to 2021) and the UK (1985 to 2021), with Bayesian hierarchical models (N-mixture models and continuous trend models). The data are national scale volunteer-collected data across Switzerland (from infofauna karch) and Britain (from Froglife) over four decades. We included nearly 4 million toad records across an average 86 populations per year in Switzerland and 1.5 million records of toads from Britain spread across an average of 80 populations per year.