<prompt> Human: I make about 100k annually. I noticed that my September paycheck didnt have as much 401K withholding as usual, and took a look at my retirement accounts... Turns out I set my pre-tax contribution amount to 23, which means I hit the 18,500 annual 401K contribution max as of my September paycheck. So the good news is that I have bigger paychecks till the end of the year, and the bad news is that if the market dips between now and then my retirement funds wont be buying into it while things are cheap or something? x200B;Im vaguely aware that this is sub-optimal, but I have no sense of perspective for how bad a problem it is. I wouldnt mind sticking the amount that wouldve gone to 401K from the rest of this years checks roughly 4,000 into some sort of post-tax retirement something-or-other, but I have no idea where to start or how to go about getting such accounts. Work set up my 401K and Roth IRA for me through Fidelity.x200B;I have 230k left on my mortgage at 3.625 interest, and in the absence of a better plan Id be inclined to just throw the extra 4k against that principal. I get the idea that an index fund would have a high likelihood of providing better returns, but at the same time actually figuring out how to use one without getting scammed or losing money seems like a lot of work compared to just owning my home sooner. x200B;I already have 3-4 months expenses in an emergency fund and work in a field with enough demand that I wouldnt be more than about 2 months between jobs even if my company disappeared tomorrow.x200B;tl;dr set contribution percentage too high and 401k hit max contribution in 9 months rather than 12. Is this a problem?  <response>: If your employer matches on a per paycheck basis and doesnt do a true up at the end of the year, you may be leaving employer match money on the table. Otherwise there isnt really anything wrong with maxing your 401k early. 