Fidelity kept track for me on all my after-tax 401k contributions. You should be able to get a yearly before/after-tax contribution listing in your Netbenefits account
If your workplace offers a ROTH 401k, you'd be better off contributing any after-tax amounts in that vehicle.
Mine were before the ROTH 401k came out, so I never had the option.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
