How much federal tax should be with held on 8400 if you claim married and one?

The amount of federal tax withheld on $8,400 can vary based on specific circumstances, including any additional deductions or credits. However, using the IRS withholding tables, if you claim "Married" and "One" allowance, your withholding might be minimal due to your income being below the standard deduction threshold. It's advisable to use the IRS Tax Withholding Estimator for a more precise calculation based on your exact situation.