Tax rates are applied to taxable income, not to adjusted gross income (AGI). Taxable income is arrived at by subtracting your personal exemptions and the standard deduction or itemized deductions from AGI. The taxable income limits for the 25% tax rate depend on your filing status.
A tax technique for receiving a refund of back taxes by applying a deduction or credit from a current tax year to a prior tax year. For example, a business net operating loss may be carried back for two years.