To determine property tax for a resale 4-room HDB flat, consider the Annual Value (AV). Tax rates from 1 Jan 2025 are: First $12,000: 0%, Next $28,000: 4%, Next $10,000: 6%, Next $25,000: 10%, Next $9,000: 14%. Example: AV $36,000 results in $960 tax. Owner-occupied flats get a 20% rebate in 2025.