I appreciate you for posting your concern here, Lora.
Federal taxes are calculated based on the details of an employee's W4 information. For the federal Income tax (or withholding), QuickBooks calculates them based on the following elements:
Taxable wages
Number of allowances/dependents
Pay frequency
Filing status
Therefore, there's no fixed amount for Federal withholding. Yet, you can consider editing the amount manually during each payroll/paycheck run. Check this article for more details about how QuickBooks calculates payroll taxes: Understand how your payroll taxes are calculated.
In addition, if you need to pay your taxes and forms electronically and run your business finances, you can visit these articles for guidance: