Biogas plants are widespread in Germany and, particularly, in the Federal State of Bavaria, where the development of renewable energy sources has been very dynamic. While biogas can substitute fossil energy carriers for producing electricity and heat, greenhouse gas (GHG) emissions are also occurring along the biogas process chain. The accounting of the GHGs produced from biogas plants is an essential step for evaluating and improving this type of energy supply. We developed an effective approach for simulating diverse biogas chains in agriculture for predicting the resulting GHG emissions in relation to energy output. This approach is executed in three stages: (1) creating a database and filling it with collected and calculated data; (2) constructing the biogas plant sample using data from the database and user’s input; and (3) running the database model for calculating and displaying the biogas plant’s GHG inventory. The database comprises information on the location and management of the farm, the sourcing and composition of the input materials / substrates, and the combined heat and power unit (CHPU) for biogas valorization. The database is connected with a web-based application model, which presents the results in graphs, numbers and percentages.