Rhythm Method
A historical calendar-only method of estimating fertile days based on past cycle lengths.
Often confused with modern NFP, the rhythm method predates real-time biomarker tracking and is significantly less reliable, especially for irregular cycles.
View the Sympto-Thermal Method profileView the The Marquette Method profileView the The Billings Ovulation Method profileView the The Creighton Model FertilityCare System profile
The rhythm method, formalized in the early 20th century, estimates the fertile window from past cycle lengths alone. It does not observe cervical mucus, basal body temperature, or hormones, so it cannot adapt to cycle variability.
Modern fertility awareness methods such as Sympto-Thermal, Billings, Marquette, and Creighton are not the rhythm method. They identify the fertile window in real time using observable biomarkers.