Catch-up on 401k for 2017
I have not hit the 18k limit on 401k last year, is there anyway to catch up on it this year before filing taxes ?
No
You could still max out 2017 contributions to your HSA and IRA if you haven't already done that
Depending on your salary, you may be able to open a tIRA and put in 5500.
Salary doesn't matter for ira
No. IRA & Roth IRA support catch up contributions until April 15 of the following year, but 401k does not.
Salary matters for traditional IRA , I think if you are join filing and above 196k then there is no deduction
What is the benefit of having a Roth IRA over investing the same amount directly via Robinhood? I am struggling to see why I would want to do this.
With Roth, the gains are tax free. If you make 5% per year over the next 40 years, all of that compound interest is tax free when you withdraw in retirement.
Other than time travel there is not much you can do.