Since you are a small business owner, you are required to pay self-employment tax. This is different from what goes on your W-4.
"If you have income from self-employment (including as an independent contractor), you will generally owe both income tax and self-employment tax. Form W-4 is primarily intended to be used by employees who are not subject to self-employment tax. Thus, like the old Form W-4, the redesigned Form W-4 does not compute self-employment tax. If you would like to use Form W-4 to make an adjustment to your withholding to account for self-employment income that you will receive from another source, use the Tax Withholding Estimator at www.irs.gov/W4app or refer to IRS Publication 505." You may also use https://turbotax.intuit.com/tax-tools/calculators/w4 to estimate your taxes.
I hope this helps.
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