Cultivation practices of white cumin (ajowan) particularly nutrient requirement differ to a certain extent in various soil and climatic conditions. A field experiment was conducted during 2007 to 2008 to determine economically feasible rate of nitrogen and phosphorus fertilization on white cumin. A treatments consisted of 4 nitrogen rates (0, 15, 30 and 45kg/ha) and 4 phosphorus rates (0, 10, 20 and 30kg/ha) was laid out in randomized complete block design with three replications planted at two locations per year. The seeds were sown in the second week of July and harvested on the last week of December. Data on plant height, and seed yield. Statistical analysis was carried out using SAS Statistical Software V8. The pooled data revealed that 45/30 N/P2O5 kg/ha fertilization recorded highest yield (whole part grounded) of 4.5t/ha over the unfertilized (2.7t/ha). Application of 45/30 N/P2O5 kg/ha gave highest net benefit (12122birr/ha) with acceptable marginal rate of return (208). Sensitivity analysis also revealed that 45/30 NP application gave the highest net benefit (9281birr/ha) with acceptable marginal rate of return (105). Fertilizer rate of 45/30 N/P2O5 kg/ha were economical rate and recommended to Takusa and similar white cumin growing areas based on this research output, but to come up with optimum rates, further study will be conducted of higher rates of nitrogen and phosphorus fertilizers.