Biodiversity Net Gain (BNG) is achieved when development projects leave the natural environment in a measurably better state than before. Under the Environment Act 2021, from November 2023, nearly all planning permissions granted in England, except for small sites, will have to include a Biodiversity Gain Plan that demonstrates the development achieves at least 10% Biodiversity Net Gain, as measured by the statutory Biodiversity Metric. BNG will be required for small sites from April 2024, and Nationally Significant Infrastructure Projects (NSIPs) from 2025. This quick guide, designed for use by Local Planning Authorities (LPAs) and developers, provides an easy-to-use checklist to help understand whether submitted Biodiversity Gain Plans are correctly completed, are feasible, and take into account their local ecological and social context.