In business and company valuation, along with the company’s income stream, the discount rate plays a key role. The main disadvantage of existing valuation methods is their inability to correctly estimate the discount rate. Currently, the only theory that allows doing this correctly is the modern theory of cost and capital structure BFO. This theory plays a fundamental role in the development of a qualitatively new approach to business valuation and company value created in this monograph. Within the framework of the BFO theory, the WACC(n) dependence is correctly estimated, which is the key point of the qualitatively new methodology for business valuation and company value developed in this monograph. Within the framework of the BFO theory, the authors of this monograph discovered the innovative effect of the company’s golden age and conducted a detailed study of it. This effect, which exists for most companies, significantly and qualitatively changes the WACC(n) dependence, which leads to a significant change in the business valuation and company value. In this and the two following chapters, we investigate the dependence of attracting capital cost on the time of life of company n at various leverage levels, at various values of capital costs with the aim of defining minimum cost of attracting capital. All calculations have been done within modern theory of capital cost and capital structure by Brusov–Filatova–Orekhova (Brusov et al., Appl Fin Econ 21(11):815–824, 2011; Brusov et al., Res J Econ Bus ICT 2:16–21, 2011; Brusov et al., Res J Econ Bus ICT 2:11–15, 2011, Brusov et al., Res J Econ Bus ICT 2:16–21, 2011; Brusov et al., Appl Fin Econ 22(13):1043–1052, 2012; Brusov et al., J Rev Glob Econ 1:106–111, 2012; Brusov et al., J Rev Glob Econ 2:94–116, 2013; Brusov et al., J Rev Glob Econ 2:94–116, 2013; Brusov et al., J Rev Glob Econ 2:183–193, 2013c; Brusov et al., Cogent Econ Fin 2:1–13, 2014; Brusov et al., J Rev Glob Econ 3:175–185, 2014b; Filatova et al., Bull FU 48:68–77, 2008). It is shown for the first time that valuation of WACC in the Modigliani—Miller theory (Modigliani and Мiller, Am Econ Rev 48:261–297, 1958; Modigliani and Мiller, Am Econ Rev 53:147–175, 1963; Modigliani and Мiller, Am Econ Rev 56:333–391, 1966) is not minimal and valuation of the company capitalization is not maximal, as all financiers have supposed up to now: at some age of the company, its WACC value turns out to be lower than in Modigliani—Miller theory and company capitalization V turns out to be greater than V in Modigliani—Miller theory. It is shown that, from the point of view of cost of attracting capital there are two types of dependences of weighted average cost of capital, WACC, on the time of life of company n: monotonic descending with n and descending with passage through minimum, followed by a limited growth. The first type takes place for the companies with low cost capital, characteristic for the western companies. The second type takes place for higher costs capital costs of the company, characteristic for the Russian companies as well as for companies from other developing countries. This means that latter companies, in contrast to the western ones, can take advantage of the benefits, given at a certain stage of development of company by discovered effect. Moreover, since the “golden age” of company depends on the company’s capital costs, by controlling them (for example, by modifying the value of dividend payments, that reflect the equity cost), company may extend the “golden age” of the company, when the cost to attract capital becomes a minimal (less than perpetuity limit), and capitalization of companies becomes maximal (higher than perpetuity assessment) up to a specified time interval.