Chemotherapy during childhood damages ovarian reserve and can affect future fertility. However, recent large epidemiological studies showed that the detrimental impact on fertility is less severe if women seek for pregnancy at a younger age. To explain this observation, we hypothesize that the detrimental effects of previous chemotherapy on the ovarian reserve may be attenuated in young adults for two main reasons. Firstly, recent evidence showed that the amount of ovarian reserve is not a critical factor for effective natural conceptions. Provided that the residual ovarian reserve allows regular ovulatory cycles, the chances of pregnancy are similar in women with intact or reduced ovarian reserve. Secondly, ovarian reserve depletion appears to be a phenomenon that is inversely related to the residual ovarian reserve rather than to age. From a mathematical perspective, this kind of regulation intrinsically attenuates the effects of an early loss of a significant amount of primordial follicles. In conclusion, the detrimental effects of chemotherapy on natural fertility may be less severe if women with a history of chemotherapy during childhood seek for pregnancy early. This information should be part of the counseling.