Calendar-based methods are not usually considered effective or useful methods of family planning among health professionals. However, new “high-” and “low”-tech calendar methods have been developed, which are easy to teach, to use, and may be useful in helping couples avoid pregnancy. The low-tech models are based on a fixed-day calendar system. The high-tech models are based on monitoring urinary metabolites of female reproductive hormones. Both systems have high levels of satisfaction. This article describes these new models of family planning and the research on their effectiveness. The author proposes a new algorithm for determining the fertile phase of the menstrual cycle for either achieving or avoiding pregnancy.