Note that there is a mandatory 20% tax withholding required on 401(k) distributions reguardless if you pay estimated tax or not.
You can make estimated tax payments using a 1040ES form or just make the payments online at: https://www.irs.gov/payments.
But note that if you expect the tax to be more than the mandatory 20% tax withholding on 401(k) distributions and/or if you are also subject to the additional 10% penalty then it is usually better to just have the 401(k) plan administrator withhold more. For example if you expect to be in the 26% tax bracket and are under age 59 1/2 then having 35% or more withheld would make estimated payments unnecessary.
Estimated tax payments for lump sum payments usually require using a 2210 form with your tax return to show the unequal income while tax withholding does not require that and is simpler.
The tax would be the same either way.
Also see:
https://www.irs.gov/newsroom/five-tax-tips-on-making-estimated-tax-payments
Any penalty would be on the total tax due on your return next April. You can pay directly on the IRS website https://www.irs.gov/payments
Be sure to pick the right kind of payment and year.....2019 Estimate
oh wait, you said 2018? Did you already file your 2018 return? Did you mean this year 2019?
Yes, sorry, I borrowed this Jan 2019 so it will be for the 2019 tax year next April.
Thank you. This was withdrawn Jan 2019, not 2018. I appreciate the advice.
@just4mar wrote:Yes, sorry, I borrowed this Jan 2019 so it will be for the 2019 tax year next April.
Borrowed?
If this was a 401(k) loan then that is not a taxable distribution unless you default on the loan. Nothing about a 401(k) loan gets reported on a tax return.