A method for valuation of a corporation or a business activity, based on a cash flow model, under which an NPV of future earnings generated by the corporation or the business activity over a term of years is calculated on the basis of a given budget for the corporation or the business activity, a given discount rate and a given budget period, which budget period is estimated by means of a calculation model based on selected factors comprising the corporation's products, market position, productive equipment and human resources, wherein a number of points are allocated to said factors on the basis of a number of data, and the points allocated to the factors are included in a mutual weighted ratio in the model applied to estimate the budget period.