Net Present Value and Internal Rate of Return were indicators used in the cost analysis of commercial poplar plantations in Serbia. The study was conducted on four types of sites under plantations of Populus x euramericana cl. I-214 aged 24–42 years. The aim was to examine the financial results of plantations of different ages at different discount rates. For a discount rate r = 12%, all the tested areas had a negative NPV, regardless of age and site quality. At r = 6%, shorter production cycles to up to 28 years of age on better site classes had positive NPV_s (80–580 €ha^-1), while at r = 4% the investments were financially justified in all cases. IRR_s varied in the range 4.32–6.94% at a discount rate of 12%. The best financial results are achieved on the best sites, with the shortest rotation cycles. Determined financial rotation length was 17 years.