<p>Although the R Shiny framework enables the development of interactive web applications without requiring advanced web programming skills, its adoption in forestry remains limited. This study presents ForestCalc, an open-source decision-support web application developed in R/Shiny for estimating forest volume, aboveground dry biomass, and carbon stocks in native forest phytophysiognomies of Minas Gerais, Brazil. The application processes user-provided forest inventory data and applies phytophysiognomy-specific allometric equations derived from the Forest Inventory of Minas Gerais, making these models accessible through a web-based environment. In addition to volume, biomass, and carbon estimation, ForestCalc incorporates phytosociological analyses to support forest assessment and management. Validation was conducted using an independent dataset from the Phytogeographic Model of the Rio Grande Basin project, comprising forest inventory measurements collected outside the dataset used to develop the original allometric equations. The results indicated good agreement between reference and estimated values, supporting the reliability of the implemented computational workflow. By integrating scientific models, inventory processing, and visualization tools into an accessible platform, ForestCalc contributes to improving the use of forest inventory information for resource monitoring, forest management, and carbon accounting in tropical ecosystems. The application also promotes the dissemination of open-source technologies and reproducible workflows in forest science.</p>