The author determines optimal production income tax rate at which net profit and state budget revenue steadily increase and a stable growth of production is ensured. For a lower rate, there is an accelerated growth in production, and for a higher rate, the budget revenue increases due to a slowdown in production growth. The author expresses the function of marginal tax rate for which net profit is absent and production has no sense. The conducted macroeconomic modeling of the development of the country’s economy in time has shown that as net profit decreases and production income tax rate increases, the amplitude and frequency of fluctuations in the variations in the real GDP vary.