KB Kookmin Bank's simulation puts the 2030 property tax rise for northern Seoul's priciest apartments at 76%

Four more annual rises of 10.3%, the pace KB Kookmin Bank's model assumes ^[3], compound to a price gain of about 48% by 2030, because 1.103 to the fourth power is 1.48 ^[1]. If assessed values move in step with market prices, the Gangnam, Seocho and Songpa bill, up 46.6%, lags the homes slightly ^[6]. The Nowon, Dobong and Gangbuk bill, up 76.1% from 753,000 won to 1.326 million won, runs well ahead of them ^[6], and the citywide average runs ahead by a smaller margin ^[4]. Divide tax growth by price growth and the northern owner pays about 19% more tax per won of home value in 2030 than this year ^[2]. The Gangnam-area owner pays about 1% less ^[3]. The report does not explain why the cheaper complexes' bills climb faster, or how it projects assessed values.

The northern bill grows fastest, or rather it grows fastest measured against the home. In won, it is the smallest increase among the district groups for which the report gives won figures. The Nowon, Dobong and Gangbuk group adds 573,000 won over four years ^[4], against 720,000 won for Geumcheon, Gwanak and Guro ^[12] and 1.639 million won for Mapo, Yongsan and Seongdong ^[5]. The citywide average adds 1.176 million won ^[10]. The steepest single case is a 109-square-meter Ssangyong unit in Dobong, whose bill goes from 570,000 won to 1.07 million won ^[9]. That is a rise of 87.7%, or 500,000 won ^[7]. All of these are base tax, before the local education tax and other surcharges ^[5].

The northern finding depends most on the growth rate. The model takes the citywide 10.3% gain recorded from January to September, a nine-month figure, and runs it forward as an annual rate ^[3]. If northern prices rise more slowly than Gangnam's, the projected northern tax rise shrinks with them. A general slowdown matters less. At 5.15% a year the average bill still rises 28.6% ^[12], against a compounded price gain of about 22%, so tax still outruns value at the average ^[8]. The ratio is the other variable. Every figure above holds it at the current 45% of assessed value ^[13]. At 60%, the northern group's 2030 bill reaches 2.63 times this year's, against 2.14 times for the sample as a whole ^[11].

I think the holding-cost point survives those tests, with one limit on how far it reaches. The sample is the five most expensive complexes in each district ^[2], so the northern figures describe the top of the northern market. The counter-view is that a fast percentage on a small base is still a small number of won, and the expensive districts keep the largest bills. Under the 50% ratio, a 112-square-meter Raemian One Bailey unit in Seocho goes from 6.76 million won to about 11 million won ^[14], an increase of about 4.24 million won ^[11].