This article proposes a conceptual framework for offset policy makers and programme administrators to shift the additionality and baseline assessment process from subjective 'tests' towards more standardised approaches based on explicitly recognised policy interventions, theories of behaviour, and objective models. This framework is intended to be applicable to any type of offset programme. A key message of this article is that offset mechanisms, to be credible, need to better define the scientific basis of additionality and baselines. And even though perfect certainty is unattainable, offset quality can be improved with clearer assumptions, better models, and greater attention to the rules of scientific inference, which are critically important when considering the use of standardised approaches.