Ethiopia's recent improvements in health outcomes benefited from the large increase in development assistance for health received in recent years, most of which supported its primary care system. Increased domestic resource mobilization for health will be needed to sustain progress given recent and likely future declines in external support. We estimate a projection model of Ethiopian government domestic resource mobilization potential compared with future health care delivery costs in order to assess Ethiopia's ability to finance its planned primary health care system. For the period of Ethiopia's current five-year health sector plan (2016-2020), the projection model indicates that if real external resources remain at the levels of 2011, domestic resource mobilization may only provide half of the estimated funds needed. Including out-of-pocket spending currently captured as retained user fees, Ethiopia is more likely to successfully finance continued delivery of primary care. Over 20 years, 2016-2035, the future sustainability of primary care services without increasing contributions from households will depend largely on significant economic growth and more government funding for primary care. Our modeling suggests that Ethiopia can substantially support further development of primary care services, even in the face of declining external support. However, it is unlikely to achieve its goals solely through "business as usual." Ethiopia is already moving forward with timely adoption of sound strategies to maintain progress. External partners should support these trends to enable transition plans to greater domestic funding with minimal disruption to positive progress that has been and is being made.