Income Taxes (US): What percentage do I get "whacked"?

Factual Questions
1

Here’s a question, that I was having trouble at work with.

Lookin’ at my pay stub, I get whacked for the following:
[ul]
[li]Federal Taxes[/li][li]FICA-Soc Security (I know the percentage)[/li][li]FICA-Medicare (I know this percentage too)[/li][li]SGLI (A flat rate, I think)[/li][li]Mid-Month Pay[/li][/ul]

I’m working on figuring out my next few months’ budgets, and am trying to predict (within a few dollars accuracy) my next few paychecks. I know the FICA-Soc Security rate is 6.2% of my base pay, and my FICA-Medicare is 1.45% of my base pay. SGLI (my life insurance policy) is a flat rate, and my mid-month pay is just a deduction for my other paycheck (I get a complete, detailed paystub every month).

I just can’t find a link or website with my Federal taxes. It seems to float around 15% or so. What the heck are the rates/deductions for taxes? I know they’re based on ‘brackets’ but I could tell you with the accuracy of a snowball in Hades what my bracket is.

Any help?

Tripler
The spreadsheet I’m writing will be available to anyone who wants a copy.

2

Federal withholding is calculated based on tables.

The tables are based on your filing status, allowance, the amout of your payroll and how often you are paid. You probably aren’t going to be able to come up with an exact to the penny number in advance however you should be able to get a good ball park.

3

You can’t just extrapolate from prior checks?

4

Hey thanks In Concievable, I’ll give that a shot!

Not really. The percentages I calculated floated around a bit, and with a 3.7% base pay raise and a promotion pay raise next month, I wanted to see if I could nail it down as close as possible.

Tripler
Much obliged, guys!