RNAV waypoints have tolerances applied during procedure construction called ATT (Along Track Tolerance) and XTT (Cross Track Tolerance), the values of ATT and XTT are generally the RNP value of the procedure, ie RNP1 gives +/- 1nm, GPS approach 0.3nm etc. The terms are defined in PANS OPS Vol II as:
"Along-track tolerance (ATT). A fix tolerance along the nominal track resulting from the airborne and ground
equipment tolerances."
"Cross-track tolerance (XTT). A fix tolerance measured perpendicularly to the nominal track resulting from the
airborne and ground equipment tolerances and the flight technical tolerance (FTT)."
The 'airborne' bit should allow for weather/aircraft issues.