wrote:
I figured out my GA state taxes by hand
[....]
from this publication.
http://www.etax.dor.ga.gov/taxguide/...xGuide2005.pdf

I am single with no (zero) allowances.

And inferentially, it appears that you are paid weekly.

I figured out my GA state taxes by hand and I could come within a few
pennies if I used the federal taxable wages, and I was over if I used
just my gross pay.
For example on one check I had $ 388.80, with 370.30 taxable
federally.

Let me clarify and correct the terminology in my first response in this
thread.

What I called "gross income" should be called "taxable gross pay (or
compensation)".
I am guessing that $370.30 is your federal "taxable gross" pay. That
is your gross pay less qualified federal pretax deductions, e.g.
employee contributions to a 401(k) or other employer pension plan and
to pretax accounts such as medical and commuter benefits. In theory,
your state's "taxable gross" pay may or may not be the same as the
federal taxable gross pay. That is the state's choice to make.
Apparently for GA, it is the same, based on your observation and based
on page 18 of the cited GA document ("Are contributions to qualified
.... plans taxable?"). I believe that is usually the case.

What I call "taxable income" is also called "wages subject to
withholding". Compare the definition of "taxable income" on page 8
with the example on page 40 of the cited GA document.

If you however, can figure a formula without taking to much of your
time, it would greatly be appreciated.

Not a problem. However, the GA instructions are poor and unclear on a
few points. The following is my interpretation. Use at your own risk.

I assume that you are looking at pages 41-43 of the cited GA document.
The GA Percentage Method is similar to the Federal Percentage Method.
You could use the formulation in my first response as a paradigm. By
the way, if you do not understand that formulation and you want an
explanation of the limits and the percentages in the formula, let me
know.

Looking at Form G-4, GA's equivalent to the Federal W-4, you declare
personal allowances (0-1 for single; 0-2 for others), dependent
allowances and additional allowances. I lump the latter two together
as "other allowances".

Thus, the gaTaxableIncome for Single Weekly can be computed by:

=gaTaxableGross - 44.25 - PersonalAllowances*51.92 -
OtherAllowances*57.50

Ostensibly, the gaWithholding might be computed by:

=1%*gaTaxableIncome + 1%*max(0,gaTaxableIncome-14.50) +
1%*max(0,gaTaxableIncome-43.50) + 1%*max(0,gaTaxableIncome-72) +
1%*max(0,gaTaxableIncome-101) + 1%*max(0,gaTaxableIncome-135)

I put that in a general form that works for all marginal tax tables.
But you might notice that 1% is a common factor in GA's case. So the
above can be simplified as follows:

=1%*(gaTaxableIncome + max(0,gaTaxableIncome-14.50) +
max(0,gaTaxableIncome-43.50) + max(0,gaTaxableIncome-72) +
max(0,gaTaxableIncome-101) + max(0,gaTaxableIncome-135))

However, that computes a tax of $15.90, whereas you correctly manually
compute $15.88. The answer lies in some anomalies of the GA table.
Consider the top taxable income of the 5% bracket, $135. The
withholding amount is (135-101)*5% + 2.74 = 1.70 + 2.74 = $4.44. That
should also be the amount to add in the 6% for taxable incomes over
$135. But GA adds $4.42 instead. There are other similar anomalies in
the Single Weekly table.

The following formula computes exactly the same withholding amount as
the Single Weekly table in the cited GA document.

=max(0, 1%*gaTaxableIncome, 2%*(gaTaxableIncome-14.50)+0.14,
3%*(gaTaxableIncome-43.50)+0.72, 4%*(gaTaxableIncome-72)+1.59,
5%*(gaTaxableIncome-101)+2.74, 6%*(gaTaxableIncome-135)+4.42)

Alternatively, combining constants:

=max(0, 1%*gaTaxableIncome, 2%*gaTaxableIncome-0.15,
3%*gaTaxableIncome-0.585, 4%*gaTaxableIncome-1.29,
5%*gaTaxableIncome-2.31, 6%*gaTaxableIncome-3.68)

It had never occurred to me that marginal rate tables might have such
anomalies. I might switch to this latter paradigm myself. (I have
been using my other formula for a very long time!)

On the other hand, you said that your figure ($15.88) differed by "a
few pennies" from your employer's figure. If the employer computed
$15.90, perhaps he is using a formula similar to my first one.