Hello, @JunNg.
Thank you for reaching out to the Community. It depends with the contribution, majority are the tax credits, earned income credit and the allowances. However, if you file a joint tax return, your federal tax rate may be lower than that of an unmarried individual. That's just one example of how U.S. tax laws are written to provide married couples with greater benefits than those received by other individuals.
To answer your other questions. You can visit the IRS website to use the Tax Withholding Estimator. This will help you make sure you have the right amount of tax withheld from your paycheck.
You may also find this IRS article helpful about the updates on the 2020 W-4 form.
For an overview of the new updates to the Federal W-4, check out this article. The information applies to all payroll versions: What’s changing with the Federal W-4?
You can also visit this IRS website to know more about the 2020 Form W-4: Publication 15 (2020), (Circular E), Employer's Tax Guide.
Just leave Reply again if you have more questions. You take care always and have a great day!
