There are many tax calculators available online from tax software developers like hrblock, to dinky town which specialize in financial calculators. These calculators vary in their features and accuracy depending on how many parameters it takes while estimating the taxes.
If you want actual amount of your taxes for 2006 then I would suggest you use one of the tax software and enter all your tax related data from all w-2, and 1099,etc. This is possible during the tax filing season as you get these tax forms. You may need to spend some time to enter all data. One advantage of using a FREE tax software like
TaxAct is that you can use it as calculator and later if you want you file your tax return, all information is already available and you just can file your tax FREE.
Now the "estimating" is often required during the oct-dec time period when you want to get some idea about your expected taxes, and you don't have all "Correct" information available. So estimation is always an approximation based on the values your provide. There are many calculators available online which requires many input parameters, which you may not know at that time period. So a simple calculator with basic information which every body will know makes more sense for general public. Again what you get from this calculator is an ESTIMATE not the actual taxes.
Our
2006 tax calculator is meant to be SIMPLE and it require only 5 parameters to calculate an estimate of 2006 taxes. YOU SHOULD NOT USE IT FOR YOUR FILING YOUR 2006 TAXES. IT IS ONLY AN ESTIMATE. You will see the same warning in all tax calculators online.