Thailand's personal income tax base is critically narrow: only 5.14 million out of 12.57 million tax filers (40.9%) actually pay tax, with 59.1% falling below the 150,000 baht exemption threshold. The tax burden is heavily concentrated—just 1% of filers contribute 50.1% of total personal income tax revenue. This structural imbalance poses a major fiscal challenge for government budget sustainability and revenue reform.