Level 42

Total Experience Required 352,649 [confirmed]

Level 100 progress: 5.17%

This is roughly:
Killing 1,176 people in Warzone, or...
Killing 1,200 people in Execution, or...
Killing 997 people in Wingman, or...
Scoring 251,893 points in Guardian, or...
Scoring 766,629 points in Annex, or...
Scoring 464,012 points in Submission.

Horde (TU4)

Completing 1,764 waves on Casual, or...
Completing 1,176 waves on Normal, or...
Completing 882 waves on Hardcore, or...
Completing 706 waves on Insane.

Or a combination of the above. Have fun!