Final answer:
An assessment of an internal revenue tax must be made within three years of either the date that the return was filed or the original due date. After this timeframe, the IRS generally cannot make any additional assessments.
Step-by-step explanation:
An assessment of an internal revenue tax must be made within three years of the later of the date that the return was actually filed or the actual (i.e., not extended) due date of the return. This means that the Internal Revenue Service (IRS) has three years from either the date the taxpayer filed the return or the original due date to assess any taxes owed. After this timeframe, the IRS generally cannot make any additional assessments, unless certain exceptions apply.