Interest rates play an important role in our market economy. As signals direct the flow of a city’s traffic through a complicated grid of intersecting streets and avenues, interest rates channel the flow of funds from savers to borrowers. To ensure the security of this flow the law states that interest rates need to be in a certain reasonable relationship with the refinancing rate of the National Bank. Then again the legal norm does not contain the definition or any numeral references regarding the difference between these two variables, a difference which is considered to be a reasonable one. Yet these are not the only questions that where fulfilled by this research, thus our scientific approach covers even the economic nature of interest rates, through by this we have intended to entirely explain their juridical form