Income Tax Withholding Formula
(I'm not making this one up, that is straight from the state manual)

1. Single Taxpayer Withholding Formulas
W is the withholding tax per pay period.
S is employee?s salary per pay period for each bracket.
X is the number of personal exemptions; X must be 0 or 1.
Y is the number of dependency credits; Y must be a whole number that is 0 or greater.
N is the number of pay periods.
A is the effect of the personal exemptions and dependency credits equal to or less than $12,500;
A=.021(((X*4,500)+(Y*1,000))÷N).
B is the effect of the personal exemptions and dependency credits in excess of $12,500;
B=.016((((X*4,500)+(Y*1,000))-12,500)÷N).

If annual wages are less than or equal to $12,500, then
W=.021(S)-(A+B).
If annual wages are greater $12,500 but less than or equal to $50,000, then
W=.021(S)+.0160(S-(12,500÷N))-(A+B).
If annual wages are greater than $50,000, then
W=.021(S)+.0160(S-(12,500÷N))+.0135(S-(50,000÷N))-(A + B)

2. Married Taxpayer Withholding Formulas
W is the withholding tax per pay period.
S is the employee?s salary per pay period for each bracket.
X is the number of personal exemptions. X must 2.
Y is the number of dependency credits. Y must be 0 or greater.
N is the number of pay periods.
A is the effect of the personal exemptions and dependenc credits equal to or less than $25,000;
A=.021(((X*4,500)+(Y*1,000))÷N)
B is the effect of the personal exemptions and dependency credits in excess of $25,000;
B=.0165((((X*4,500)+(Y*1,000))-25,000)÷N).

If annual wages are less than or equal to $25,000, then
W=.021(S)-(A+B).
If annual wages are greater $25,000 but less than or equal to $100,000, then
W=.021(S)+.0165(S-(25,000÷N))-(A+B).
If annual wages are greater than $100,000, then
W=.021(S)+.0165(S-(25,000÷N))+.0135(S-(100,000÷N))-(A+B).

Note(s):

• All amounts are annual unless otherwise noted