Biodiversity offsetting is increasingly being used to reconcile the objectives of conservation and development. It is generally acknowledged that there are limits to the kinds of impacts on biodiversity that can or should be offset, yet there is a paucity of policy guidance as to what defines these limits and the relative difficulty of achieving a successful offset as such limits are approached. In order to improve the consistency and defensibility of development decisions involving offsets, and to improve offset design, we outline a general process for evaluating the relative offsetability of different impacts on biodiversity. This process culminates in a framework that establishes the burden of proof necessary to confirm the appropriateness and achievability of offsets, given varying levels of: conservation concern for affected biodiversity; residual impact magnitude; opportunity for suitable offsets; and feasibility of offset implementation in practice. Rankings for biodiversity conservation concern are drawn from existing conservation planning tools and approaches, including the IUCN Red List, Key Biodiversity Areas, and international bank environmental safeguard policies. We hope that the proposed process will stimulate much-needed scientific and policy debate to improve the integrity and accountability of both regulated and voluntary biodiversity offsetting.