Bioaccumulation (B) assessments using various methods, data, metrics, and classification criteria are routinely conducted as a part of chemical regulatory programs. B assessments are challenging because of limitations on the availability of reliable and representative empirical data. Here, we present tiered and iterative methods for B assessment to address uncertainty and reduce unnecessary animal testing. The Bioaccumulation Estimation Tool (BET) is a screening-level modelling system integrated in the Exposure And Safety Estimation (EAS-E) Suite platform. The BET includes mass balance bioaccumulation models for a diverse range of representative ecological receptors (plants, invertebrates, fish, birds, and mammals) and food webs (aquatic and terrestrial). Typical laboratory test animals are also included, i.e., fish and rat. The BET is automatically parameterized in the EAS-E Suite platform requiring only chemical name, CAS or SMILES notation as input. Users can easily refine the default input parameters with preferred partition coefficients (including options for biological-phase partitioning), biotransformation rates (including in vitro rates from S9, hepatocyte or microsomal assays) and dietary absorption efficiencies. The BET calculates B metrics such as lab fish and invertebrate Bioconcentration Factor (BCFs), field Bioaccumulation Factors (BAFs) for invertebrates and fish as well as lab and field fish and homeotherm Biomagnification Factors (BMFs) based on uptake, accumulation, and elimination kinetics (i.e., total elimination half-life). The same screening-level models in the BET are included in the Bioaccumulation Assessment Tool (BAT). The BAT provides guiding principles to collect, generate, evaluate, and integrate various Lines of Evidence (LOE) (in silico, in vitro, lab and field studies) for a more comprehensive weight-of-evidence approach for B assessment. A case study showing the applicability of the BET and the BAT for the B assessment is presented. The BET and the BAT are freely available and can be readily used by interested stakeholders within the regulatory community.