To calculate the monthly federal income tax (FIT) withholding for 2025, we first determine the monthly gross pay: $\$24,000 / 12 = \$2,000.00$. Next, we subtract the pretax medical insurance, which is exempt from FIT: $\$2,000.00 - \$27.00 = \$1,973.00$ (Union dues are post-tax and do not reduce taxable income). Using the 2025 percentage method for a Single filer with Step 2 unchecked, we account for the standard deduction. For a monthly period, the first portion of income (approximately $\$1,250$ in 2025) is taxed at 0% due to the standard deduction. The remaining taxable amount of roughly $\$723$ is taxed at the 10% bracket. After applying the specific IRS 15-T tables and banding, the resulting withholding is $\$72.30$. Accurate manual calculation is a vital skill for payroll professionals to audit system accuracy and handle manual adjustments for employees with lower annual earnings who may still have a tax liability.