Final answer:
The IRS generally has a three-year window to assess an additional tax liability against a taxpayer after the filing of a tax return, with some exceptions for underreporting or fraud.
Step-by-step explanation:
The general timeframe in which the Internal Revenue Service (IRS) may assess an additional tax liability against a taxpayer after the filing of an income tax return is typically within three years. This period is known as the statute of limitations for tax assessments. However, there are exceptions to this rule, such as cases of substantial underreporting of income or fraud, which may extend the period the IRS can audit and assess taxes.