Wildlife-vehicle collisions (WVC) can result in property damage, injury and death to drivers. WVC can similarly cause wildlife injury and mortality, genetic fragmentation and other population impacts. State departments of transportation evaluating the need to reduce WVC use evidence of WVC and other data to inform mitigation decisions. Mitigation infrastructure, such as wildlife crossings with exclusion fencing, are effective measures for reducing WVC. Yet, states generally lack consistent econometrics for evaluating the benefits of reducing WVC relative to the costs of mitigation. They also lack freely-available tools based on contemporary principles of benefit-cost analysis to plan for WVC mitigation, especially tools that allow them to update analyses as new data are collected. To meet these needs, we developed a web-based tool (https://www.wildlifecrossingcalculator.org) to assist decision-making related to WVC mitigation, based on economic benefits and costs associated with WVC and mitigation activities. The tool was based on the premise that “benefits” are the sum of avoidable costs (e.g., reduced crashes involving wildlife) and “costs” are the sum of response costs, such as constructed mitigation. We collaborated with transportation and wildlife staff from 5 US states (AZ, ID, MT, OR, WY) to elucidate goals for such a decision-support tool, develop wildlife values, estimate crash costs, and calculate costs for different types of mitigation. The tool estimates the total costs (wildlife cost + crash cost) for individual WVC events, which can then be summed to a roadway segment (e.g., 1 mile section). The user can then compare the benefit of avoiding the costs of WVC with potential costs of mitigation by selecting from a menu of typical mitigation items (e.g., wildlife crossing structure). We demonstrated the econometric tool using WVC data for California and local examples where WVC mitigation would potentially be compensated by benefits from reduced rates of WVC. The timeframe and degree to which benefits outweighed costs varied with the highway segment (and therefore WVC conditions), type of structure, and discount rate used. To date, analysts in 28 agencies in 18 states have signed up for accounts on the WCC and so far have completed 58 statewide and regional hotspots analyses and 23 mitigation cost and benefit-cost analyses. This suggests that the tool could be broadly useful to states seeking decision-support for WVC mitigation. Its modular structure also allows other types of information and sub-routines to be incorporated (e.g., successful wildlife movement). The freely-available Wildlife Crossing Calculator platform provides flexibility and transparency in comparing the fiscal benefits and costs of potential mitigation investments to support how states prioritize and incorporate WVC reduction projects into transportation planning.