taxes how to calculate not sure how?

[MinhT1]

TurboTax calculates the tax from the IRS tax tables.

The tax tables gives a tax amount for a $25 or $50 range of taxable incomes.

For example, if you file Single, your tax liability is $15,024 for taxable income between $90,750 and $90,800.

The formula will give a number which can be off by a few dollars depending on where in the $50 range your actual taxable income is.

[VolvoGirl]

What taxes are you asking about?  You don't need to calculate it yourself.  That's what Turbo Tax does.  

There are like 7 different ways to calculate the tax.
It depends what kind of income you have. Even though the full amount shows up in the total income on the 1040 line 7, if you have capital gains or qualified dividends the tax is not taken from the tax table but is calculated separately from Schedule D. The tax will be calculated on the Qualified Dividends and Capital Gain Tax Worksheet. It does not get filed with your return. In the online version you need to save your return as a pdf file and include all the worksheets to see it.