Section 10(1) of the Invention Promotion Act prescribes that if the inventor employee owns patent of the employee invention, the employer company owns free non-exclusive right of the employee invention. (Under the current case law) Based on the provision, the company’s profit, used for calculating employee invention remuneration, is calculated by deducting the profit which the company would have achieved from the free non-exclusive right from the profit which the company would have achieved from the patent exclusive right. Exclusive right contribution rate (hereinafter “ERCR”) is defined as rate of exclusive revenue and excess revenue. Here exclusive revenue means revenue based on patent right and excess revenue means exclusive revenue minus revenue based on non-exclusive right. In Japan, it is called as excess revenue rate. This paper has explored calculation jurisprudence on ERCR. As results of such explore, the followings have been found. Firstly, in Korean and Japanese cases, our authors have failed to find a case which clearly understood concept of ERCR and clearly applied the concept to the given fact patterns. Secondly, the paper has suggested a new method, which calculates ERCR based on rate of exclusive right royalty and non-exclusive right royalty. Thirdly, in the same parties and the same circumstances, exclusive royalty rate is about two times bigger than non-exclusive royalty rate. Fourthly, under a normal situation where the defendant company’s market share as non-exclusive licensee is 50% and exclusive royalty rate is about two times bigger than non-exclusive royalty rate, ERCR is 75%. Fifthly, the court on the one hand should remember such 75% number as an important reference, and on the other hand should further try to find (1) difference of exclusive right royalty rate and non-exclusive right royalty rate and (2) the defendant company’s hypothetical market share as a non-exclusive licensee.