The Property Sales Campaign is aimed at those selling homes in the UK or abroad, where CGT should be paid on any profits made.
This includes, for example, properties people have sold that were given to them and the sale of holiday homes.
People will have until 9 August to tell HMRC about any unpaid tax on property sales and until 6 September to pay the tax owed.
HMRC says people who come forward voluntarily will receive lower penalties but warns after 6 September it will take a much closer look at the tax affairs of those who have sold properties other than their main home, but who appear to have paid no CGT.
HMRC head of campaigns Marian Wilson says: “It is better to come to us before we come to you. After the opportunity closes on 6 September, HMRC will use information it holds about property sales in the UK and abroad to identify people who have not paid what they owe. Penalties – or even criminal prosecution – could follow.”