Your listing can remain on the HDB Flat Portal as long as you have a valid Intent to Sell, until you grant an Option to Purchase (OTP) to a buyer. As granting an OTP has committed you to selling the flat to a specific buyer and not to others, unless the OTP has lapsed without the buyer exercising it, please deactivate your flat listing.

HDB will automatically deactivate your listing after we have receive a Request for Value or resale application for your flat. Your listing will be removed after the sale of your flat is completed or your Intent to Sell has expired, whichever is earlier.

This information is sourced from HDB.