Here is a list of Civil 3D Version numbers and AutoCAD Version Numbers:
Civil 3D 2011 "8.0" AutoCAD R18.1
Civil 3D 2012 "9.0" AutoCAD R18.2
Civil 3D 2013 "10.0" AutoCAD R19.0
Civil 3D 2014 "10.3" AutoCAD R19.1
Civil 3D 2015 "10.4" AutoCAD R20.0
Civil 3D 2016 "10.5" AutoCAD R20.1
Civil 3D 2017 "11.0" AutoCAD R21.0
Civil 3D 2018 "12.0" AutoCAD R22.0
Civil 3D 2019 "13.0" AutoCAD R23.0
Civil 3D 2020 "13.2" AutoCAD R23.1
Civil 3D 2021 "13.3" AutoCAD R24.0
If the pattern holds, then the numbers for the next version should be:
Civil 3D 2022 "13.4" AutoCAD R24.1
