How much is tax if I start an Individual 401(k) Plan? There is no earnings/income for this year 2021. thanks

[Niyo1]

spouse has a job and income though.

[DoninGA]

If you do not have any earned income from self-employment then you cannot contribute to a one-participant 401(k) plan

[Opus 17]

To start a solo 401(k), you must be self-employed and filing a schedule C, and your maximum contributions can't exceed your net business income. (Plus many other rules.)

If you are married and file a joint return, you can contribute into an IRA in your name from your spouse's earning, the IRA contribution limit is $6000.  Whether you get a tax deduction for that contribution depends on your total income (you plus your wife) and whether your wife is covered by a retirement plan at work.  See this page.

https://www.irs.gov/retirement-plans/2021-ira-deduction-limits-effect-of-modified-agi-on-deduction-i...

You may also be eligible to contribute to a Roth IRA.

Remember that even though a 401(k) and other workplace qualified plans are similar to IRAs, they are controlled by different sections of the tax code and some of their rules are very different.