<prompt> Human: Hey PFI left a previous employer at the end of October with over 15K contributed to a 401K for 2017. I started a new job the next day and am already contributing to another 401k both are via Fidelity, both comapanies use ADP. I set a very aggressive 401k contribution at the new company - however does there exist a safeguard or mechanism to keep me from blowing past 17.5K or 18K this year?What happens if I overcontribute in 2017?  <response>: There is no mechanism to prevent this, you need to manage your contributions. If you over contribute, I believe you can elect to have some counted as an non-deductible contribution, but you should check with an accountant. If you do over contribute and the IRS finds out, which they will, youll have to withdraw the over-contribution plus any investment gains and then pay the taxes and a penalty on the amount. 