Lol ya i figured. To answer your question though, I do know what you are saying and the calculation is kind of what i said in my original response. This is assuming that you are given 4 different income levels at 4 different dates (the dates probably would be around the end of each quarter).
For the first installment you have to annualize the income - (Net Income through first date (income-deductions)/#of months in the first date)*12.
This gives you your annualized income as of the first quarter (assuming there are 4 dates). Multiply that by 39% (top rate for corporations/ 35% top rate for individuals) If no rate is given, if a rate is given use the given rate. This is the total annual tax due. For individual you would multiply this by 90% (unless AMT then 110%) for corporation multiply this by 100%. After you multiply by 90% or whatever you need to divide this number by the amount of installments that are left to be paid. In this case the first one would be divided by 4 assuming there are 4 installments due.
For the next and subsequent installments you would do the same thing. Annualize the income, multiply by the applicable top tax rate to find total tax due. Multiply then by 90%, 100%, 110% depending on taxpayer (Ind or Corp). THEN subtract out any tax payments made in previous installments from earlier in the year. This number after all that is the remaining tax left to be paid. Divide the remaining tax left to be paid by the number of installments left to be paid and this is your installment payment. In the second quarter assuming there are 4 installments required, you would divide it by 3.
Do this for the rest of them and that is how you figure out quarterly installment amounts.
1 income level is much easier to do you just then take the income subtract any deductions. Multiply by the appropriate tax rate. Then multiply by 90% and divide by required installments. This gets you amount to be paid with each installment.
Hope this helps, It is hard to help you cuz i dont really have an example to walk you through
FAR - 88 (Jul 2012)
AUD - 85 (Oct 2012)
BEC - 82 (Nov 2012)
REG - 92 (Jan 2013) DONE!
Using Becker Self Study 2012