How to enter credit for planned qualified retirement savings contributions for 401k

[Wall-E]

I want to see the effect of a planned 401K contribution so I can make the correct payment of taxes on 4/15/2019 for the amount expected to be due after the 401K contribution is credited?

[RBBrittain]

401(k) contributions are deducted from your W-2, not elsewhere on your return. Thus, 401(k) contributions made now won't affect the 2018 return you file tonight; they will show up on your 2019 W-2 you will get at the start of next tax season.

If you're looking for the impact of a 401(k) contribution on your 2019 withholding, try the IRS withholding calculator at https://www.irs.gov/individuals/irs-withholding-calculator . If you are paying 2019 estimated taxes, fill out the worksheets for a new 1040-ES at https://www.irs.gov/pub/irs-pdf/f1040es.pdf .