Fertility information is an important component of comprehensive sexuality education, but the extent to which adolescents are taught or informed about fertility is unknown in Australia. This study examined knowledge of fertility using an anonymous, online survey of > 2,600 adolescents aged 15-18 across Australia. Respondents represented diverse backgrounds, including sexuality and gender diversity (>60% identifying other than heterosexual, 17% gender identity other than man/woman). Average knowledge of fertility was significantly poorer compared to average knowledge of reproductive and sexual health content linked to the national curriculum (p < 0.001). Linear regression and LASSO variable selection modelling identified significant, but small associations between some sociodemographic factors and knowledge about fertility or overall reproductive and sexual health. Over 80% of respondents considered their sexual health education insufficient, which was associated with poorer knowledge on all outcomes measured in linear regression models. These findings suggest that including fertility content explicitly within the Australian national curriculum will likely increase adolescent understanding of fertility. The strong participation of the adolescent LGBTQ+ community in the survey demonstrates their interest in contributing to reproductive and sexual health education reform. Inclusivity, particularly of sexuality and gender should be a key consideration in reproductive and sexual health education delivery in Australia.