If you haven't filed your 2020 return yet, use the power of TurboTax to generate a new W-4 form. The link has instructions. The W-4 calculations in your program are up to date with current tax rates.
If you have already filed, you can use Tax Caster to do the same thing. You are going to enter all of your estimated income for 2021 and TurboTax can help determine the best withholding options for federal tax from your spouse's job. When you click on the link, it says 2019, but the questions are asked for 2021, so disregard the title of the page.
Each state has its own tax laws, so find your state on this chart to visit their website where you can get the state equivalent W-4 form and update it for her employer.
How to adjust your W-4 withholding - Helpful article that expands on updating your withholdings on Form W-4.
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