Planning and/or drilling wellbores. At least some of the various embodiments are methods including: receiving data indicative of position of a first wellbore; reading data indicative of position of an offset wellbore; reading data indicative of a fracture diameter for the offset wellbore; calculating a first positional uncertainty of the first wellbore; calculating a second positional uncertainly of the offset wellbore taking into account the data indicative of position and the data indicative of fracture diameter; and generating a value indicative of proximity of the positional uncertainties.