Abstract: Estimating and predicting wellbore tortuosity. At least some of the illustrative embodiments are methods including: receiving, by a computer system, an indication of rotational drilling time and slide drilling time for a wellpath; calculating a value indicative of tortuosity for the wellpath based on the indication of rotational drilling time and slide drilling time for the wellpath; determining, by the computer system, that the wellpath exceeds a tortuosity threshold, the determining based on the value indicative of tortuosity; and changing a drilling parameter regarding the wellpath responsive to determining that the wellpath exceeds the tortuosity threshold.