The ATO will use data-matching as it looks closely at gains from disposals of shares, property and cryptocurrency.
Records relating to any capital gains tax (CGT) event should be kept for at least five years after the year in which the event occurred. Records should also be kept of any net capital losses, which could offset against capital gains in a later year.
Once a loss is offset against a capital gain, records of the CGT event that resulted in the loss should be kept for two years (for individuals and small businesses), or four years (for other taxpayers).
From CAP TAX News – 15 October 2020 / Edition 40