Net additions to stock (NAS) are an indicator based on economy-wide material flow accounting and analysis. NAS, a measure of the physical growth rate of an economy, can be used for estimates of future waste flows. It is calculated using two methods: The indirect method of calculation is a simple difference between all input and output flows, whereas the direct method involves measuring the amounts of materials added to particular categories of physical stock and the amounts of waste flows from these stocks. The study described in this article had one leading objective: to make available direct NAS data for the Czech Republic, which could later be used for predicting future waste flows. Two additional objectives emerged from the first: (1) to develop a method for direct NAS calculation from data availability in the Czech Republic; (2) to calculate NAS directly, compare the results with those achieved in indirect NAS calculation, and discuss the identified differences. The NAS for the Czech Republic calculated by the direct method is equal to approximately 65 million tonnes on average in 2000-2002 and is approximately 27% lower than the NAS acquired by the indirect method of calculation. The actual values of directly calculated NAS and its uncertainties suggest that the indirect NAS is more likely to be an overestimation than an underestimation. Durables account for about 2% of the total direct NAS, whereas the rest is attributed to infrastructure and buildings. The direct NAS is dominated by nonmetal construction commodities such as building stone and bricks, which equal approximately 89% of the total direct NAS. Calculation of NAS by the direct method has been proved to be feasible in the Czech Republic. Moreover, uncertainties related to direct NAS are lower than those related to indirectly acquired NAS.