The aim of the present article is to research the availability of rules in the change of the prices of the most spread flats in the neighbourhoods of Sofia. The results from a research in the change of the offered prices of the residential real estates by months for an annual period of time (from October 2016 to September 2017) have been presented. The presence of an uprising tendency for the bigger share of the neighbourhoods has been proven. For those of them where there is a tendency missing are calculated indices for seasonality by the method of the mean chronological value. Upcoming seasonal deviations of the mean monthly prices from the average annual by the separate types of flats (studios, one-bedroom and two-bedroom flats), whereas the highest values are registered in the summer and the early autumn - the months August and September, and the lowest in the late autumn - the months October and November. The most significant are the fluctuations in the variation of the prices in the studios, followed by the two-bedroom flats and one-bedroom flats. The results could be useful to some potential investors.