In a good market next year, let’s assume your HDB fetches 6% more.
$500,000 x 6% = $30,000
You gain an extra $30,000.
Now you upgrade to a 2-room private property at $1,200,000 and it costs 9% more.
$1,200,000 x 9% = $108,000
It is proven that in a good market, you will end up paying more to upgrade your assets