Net primary production (NPP) is a critical ecosystem property that researchers and land managers attempt to quantify across ecosystems globally. Although the belowground NPP (BNPP) component of total NPP often contributes 50% or more to total NPP, it is infrequently measured due to the amount of labor involved. Here, I present a rapid method to estimate BNPP or fine root production in rangelands using sequential or root ingrowth cores and modifications to existing root-washing methods. The details provided should allow anyone to estimate BNPP in rangelands worldwide with minimal investment in materials and labor.