如果继续upgrade去二手组屋，第一套组屋必须在6个月内卖掉。

如果upgrade去公寓，现有政策下PR组屋屋主也必须在exercise OTP之前通知政府，然后再6个月内把组屋卖掉。

怎么算，最终只能有一套房子。不过IRAS网站只提到PR买卖组屋只算5%ABSD。公寓的话最好要确认，因为PR买公寓必须卖掉组屋是HDB的规定，不是IRAS的。

ABSD remission is granted in the following scenarios : -

(i) For purchase of HDB flat/new EC by a household which comprises SC(s) and SPR(s) co-owners
(ii) For purchase of HDB flat/new EC in cases where HDB grants the household a 6-month or such other period as may be stipulated by HDB to dispose of its existing property(ies)
(iii) A lower ABSD rate of 5% (instead of 10%) will apply for purchase of HDB flat by SPR household where HDB grants the SPR a 6-month or such other period as may be stipulated by HDB to dispose of the existing property(ies)

Remission for such purchases will be granted automatically upon approval of purchase by HDB. No separate application to IRAS or HDB is required.

来自： http://www.iras.gov.sg/irasHome/page04.aspx?id=12822