A widely used methodology for estimating the beta of companies with the Capital Asset Pricing Model (CAPM) uses comparable firms based only on industry or sector classifications (Bancel, F., and U. R. Mittoo. 2014. “The Gap between the Theory and Practice of Corporate Valuation: Survey of European Experts.” Journal of Applied Corporate Finance 26, no. 4 (Fall): 106–17. doi:https://doi.org/10.1111/jacf.12095, 112; KPMG. 2017. “Cost of Capital Study 2017: Diverging Markets, Converging Business Models.” Accessed September 28, 2018. https://assets.kpmg.com/content/dam/kpmg/ch/pdf/cost-of-capital-study-2017-en.pdf, 37). We hypothesize that even within industries, there is a significant relationship between the cost of equity and the life cycle of a firm. We argue that these variables are correlated because different life-cycle stages exhibit different degrees of systematic risk. Therefore, as the firm moves along its life cycle, its unlevered beta decreases. We define the stages of the firm life cycle based on a modification of the theoretical typology of (Miller, D., and P. Friesen. 1984. “A Longitudinal Study of the Corporate Life-Cycle.” Management Sciences 30 (10): 1161–83. http://www.jstor.org/stable/2631384, 1162–3) and then classify a sample of listed companies into these stages using (Dickinson, V. 2011. “Cash Flow Patterns as a Proxy for Firm Life-Cycle.” The Accounting Review 86 (6): 1969–94. doi:https://doi.org/10.2308/accr-10130) cash flow statements methodology. We construct value-weighted portfolios that are formed based on our life-cycle stages classification, adapting the procedure of (Fama, E., and K. R. French. 1993. “Common Risk Factors in the Returns on Stocks and Bonds.” Journal of Financial Economics 33 (1): 3–56. doi:https://doi.org/10.1016/0304-405X(93)90023-5). Finally, we compare the betas (levered and unlevered) of these portfolios to determine whether there are statistically significant differences. Our results show clear evidence of a relationship between betas and the corporate life cycle and that this relationship is robust to both changes in the period of analysis and omitted variables bias (when controlling with the four-factor model of (Carhart, M. M. 1997. “On Persistence in Mutual Fund Performance.” The Journal of Finance 52 (1): 57–82. doi:https://doi.org/10.1111/j.1540-6261.1997.tb03808.x). We believe our results show an important shortcoming in a widely used methodology among practitioners for estimating the CAPM.