Got a w-2 and a 1099-misc. I contributed $6500 to a IRA. Can I also contribute to a solo401k and deduct it?

[JohnW15]

You can't make a 401k contribution now for your 2018 tax return, before the April 15th filing deadline, that would be based on the Form W-2 income from last year.

401k elective deferrals must be made through payroll deduction by the end of the tax year.  There's no grace period after that to make additional contributions.