Under the current Tax Administration Law, the DGT can issue an underpaid tax assessment letter for the years up to 2007 only within ten years after the incurrence of a tax liability, the end of a tax period (month) or the end of (part of) a tax year, but no later than 2013. For years from 2008 onwards, the time spans for the issuing of underpaid tax assessment letters is reduced to five years.

Once a tax assessment letter for a particular tax of a particular month or year has been issued, additional tax assessment letters may still be issued within the specified time limits (five or ten years depending on the tax years) to the extent there is new data (novum) or information which was not disclosed (or not adequately disclosed) in the tax returns and/or during tax audits. The issue of an Additional Underpaid Tax Assessment Letter (Surat Ketetapan Pajak Kurang Bayar Tambahan SKPKBT) calls for a 100% surcharge on the tax due as an administrative penalty. However, a taxpayer may avoid the surcharge if they voluntarily notify the DGT of the novum or the undisclosed information.

The tax due reported in a tax return is considered certain if no tax assessment letter is issued within the specified time limit. Nevertheless, a SKPKB or SKPKBT can still be issued beyond the specified time limit to a taxpayer who, by virtue of a court verdict, is found guilty of a taxation crime after the specified time limits. A SKPKB or a SKPKBT issued in such a situation will include an interest penalty totaling 48% of the underpaid tax.