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Calculating Income Tax: The Tax Formula

Updated on January 31, 2015

The Tax Formula for Individuals:

This is just a basic explanation of the tax formula for individual tax payers. I hope someone can find this information useful when trying to understand taxes better.

Individual tax payers calculate their tax in accordance with a tax formula. Understanding the formula is important, since all tax determinations are based on the result. The formula is as follows:

-DEDUCTIONS FOR AGI (adjusted gross income)
x TAX RATE (using appropriate tax tables or rate schedules)

Gross Income:

The calculation of taxable income begins with gross income. Gross income includes ALL income, unless the tax law provides for a specific exclusion.

Deductions for Adjusted Gross Income:

The first category of deductions includes the deductions for AGI. These deductions include student loan interest, a tuition and fees deduction, certain educator expenses, alimony payments, trade or business expenses, certain reimbursed employee business expenses paid under an accountable plan, moving expenses, the penalty on early withdrawal from savings, and contributions to qualified retirement plans. I am not going to go into detail about these deductions however if I can provide more detail in a later hub if enough people request it.

Adjusted Gross Income:

The amount of adjusted gross income is sometimes referred to as the “magic line”, since it is the basis for several deduction limitations. For example, the limitation on medical expenses is one. A taxpayer’s AGI is used to determine the phase-out of the otherwise allowable itemized deductions and personal dependency exemption amounts.

Standard Deduction or Itemized Deductions:

Itemized deductions are personal items that congress has allowed as deductions. Included in this category are medical expenses, certain interest expenses, certain taxes, charitable contributions, casualty losses, and other misc. items. Tax payers should itemize their deductions only if the amount exceeds the standard deduction amount. The table below gives the standard amounts for 2014.


The personal exemption and the dependency exemption for 2014 is $3,950. Keep in mind that there is a Phase-out tax bracket for high-income families. (This can also be discussed in detail in a later hub if requested)

The Gross Tax Liability:

A tax payer’s gross tax liability is obtained by reference to the tax table or use of a tax rate schedule (which is provided below). Tax credits and prepayments are subtracted from gross tax liability to calculate the net tax due the government or the refund due the tax payer.

2014 Tax Brackets

Married Individuals Filing Joint Returns and Qualifying widow/widower:

Tax rate: 10%

Single filers: Up to $9,075

Married filing jointly or qualifying widow/widower: Up to $18,150

Married filing separately: Up to $9,075

Head of household: Up to $12,950

Tax rate: 15%

Single filers: $9,076 to $36,900

Married filing jointly or qualifying widow/widower: $18,151 to $73,800

Married filing separately: $9,076 to $36,900


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      Olaf 3 years ago

      I think you meant to ask if your health iunarnsce premiums are taken out of your check before or after tax. In the United States, almost all companies take out the premiums pre-tax because this costs you less. (For example, if your gross pay is $ 100, your tax rate is 20%, and your premiums are $ 30, you would have $ 50 of net pay if your premiums were taken out after tax [(100 x 80%) - 30 = 50] but you would have $ 56 of net pay if premiums were taken post-tax [(100-30) x 80% = 56].Hope that helps!