Illegal fishing has been a significant threat to sustainable capture fishing all around the world with no exception to fish stocks in the Arafura and Timor Seas (ATS). Although the ATS countries have different law enforcement abilities and capacities, they share a common goal to combat illegal fishing, especially illegal fishing crimes. In adopting strategic and effective policy to combat illegal fishing the countries need a solid information base to evaluate previous data to develop evidence-based policies. This research developed an updated formula to estimate the avoided volume and value losses from illegal fishing in the ATS countries from 2016 to 2019 to support effective policy development. The data shows how each country has different rates and types of illegal fishing. Thus, with the derived formulas, the ATS countries have been able to adopt evidence-based policy in combatting illegal fishing in accordance with the need of the countries’ current situation. The ATS countries can now evaluate and adjust their policy from time to time to ensure sustainable fishing in ATS with the intention that the improved policies can lead to more effective enforcement of the fishing laws to combat and reduce illegal fishing.