Calculation. To figure out how much a traditional IRA will save on taxes, look at your taxable income before you deduct your traditional IRA contribution. The amount will put you into one of six tax brackets. The more you make, the higher the tax rate is.alculation. To figure out how much a traditional IRA will save on taxes, look at your taxable income before you deduct your traditional IRA contribution. The amount will put you into one of six tax brackets. The more you make, the higher the tax rate is.