Level 87

Total Experience Required 4,403,270

Level 100 progress: 64.51%

This is roughly the same as:

Killing 7,339 people in Warzone, or...
Killing 7,489 people in Execution, or...
Killing 6,220 people in Wingman, or...
Scoring 1,572,597 points in Guardian, or...
Scoring 4,786,164 points in Annex, or...
Scoring 2,896,889 points in Submission.

Horde (TU4)

Completing 11,009 waves on Casual, or...
Completing 7,339 waves on Normal, or...
Completing 5,505 waves on Hardcore, or...
Completing 4,404 waves on Insane.

Or a combination of the above. Have fun!