These tables were derived from Publication 15, Circular E, Employer's Tax Guide
from the IRS. If you know the total amount you want to withhold, you can subtract the amount which will be withheld
based on marital status and number of exemptions to give an additional withholding amount. If these tables change in subsequent years
you will be at least partially protected if you don't change your withholding preference. The marginal tax bracket and calculated
withholding are displayed for zero thru seven exemptions for both single and married taxpayers.
All calculations are done at the annual level (allowable per above publication) and may not be exact due to roundoff error. For example
on page 41, an unmarried employee is paid $800 weekly. This employee has in effect a Form W-4 claiming two withholding
allowances. This gives $81.43 using weekly tables and $81.42 here, but could be off by several cents.
The following example, from page 44, is from that publication and reproduces its final answer:
Annual income tax withholding. A married person claims four withholding allowances. She is paid $1,000 a week.
Multiply the weekly wages by 52 weeks to figure the annual wage of $52,000. Subtract $16,000 (the value of four withholding allowances
for 2015) for a balance of $36,000. Using the table for the annual payroll period on page 46, $3,187.50 is withheld. Divide the annual
tax by 52. The weekly income tax to withhold is $61.30.
If you are experimenting with your annual estimated income from all sources, you may enter it in the "Salary or Pension" field,
but then check "No Multiply". For example, someone married claiming four exemptions earns $1200 twice a month plus an additional $3000
each year, but nothing is withheld from the $3000. Entering $1200 semi-monthly gives $17.50 to be withheld and an annual salary of $28,800.
To arrive at an additional amount to withhold, enter 31800 as the salary while checking "No Multiply" for a value of $30.00 to withhold.
When redoing the original salary, the taxpayer could specify Married & 4 with 12.50 additional withheld or Single & 5 and $2.92 additional
withholding per pay period.