Financing is becoming increasingly important as the cost of immunizing the world's children continues to rise. By 2015, that cost will likely exceed US$60 per infant as new vaccines are introduced into national immunization programs. In 2006, 51 lower and lower middle income countries reported spending a mean US$12 per surviving infant on routine immunization. By 2012, the figure had risen to $20, a 67% increase. This study tests the hypothesis that lower and lower middle income countries will spend more on their routine immunization programs as their economies grow. A panel data regression approach is used. Expenditures reported by governments annually (2006-12) through the World Health Organization/UNICEF Joint Reporting Form are regressed on lagged annual per capita gross national income (GNI), controlling for prevailing mortality levels, immunization program performance, corruption control efforts, geographical region and correct reporting. Results show the expenditures increased with GNI. Expressed as an elasticity, the countries spent approximately $6.32 on immunization for every $100 in GNI increase from 2006 to 2012. Projecting forward and assuming continued annual GNI growth rates of 10.65%, countries could be spending $60 per infant by 2020 if national investment functions increase 4-fold. Given the political will, this result implies countries could fully finance their routine immunization programs without cutting funding for other programs.