Background Although 90% of babies <1500 g (very-low-birth-weight or VLBW) are appropriate for gestational age (AGA) at birth, almost all are small for gestational age at 36 weeks of gestation, mainly due to nutritional deficiency in the first weeks of life. A computer calculation program (CCP) to calculate parenteral nutrition (PN) was introduced to improve nutritional intake in preterm infants. Methods Somatometric data and composition of PN of VLBW infants were compared with two points of time measured over a period of 4 years. Results Data from 56 patients born before the introduction of the CCP (2001-2002) and 59 patients born after the introduction of the CCP (2004-2005) were obtained. Although the number of AGA infants at birth did not differ, the computer-calculated group had significantly more AGA infants at the time of discharge from hospital (44% vs. 14%, p < 0.05). In this group, more protein and fat were administered in the first 5 days of life (7.3 g/kg vs. 4.5 g/kg, p < 0.05 and 5 g/kg vs. 0.5 g/kg, p < 0.05) and the duration of total PN was shorter (16 days vs. 24 days, p < 0.05). Conclusion Because the CCP contributes to a better weight gain in VLBW infants due to simplification of PN calculation, we suggest its use in the calculation of PN in VLBW infants.