The related payments rule applies to arrangements entered into after 7.30pm (Australian Eastern Standard Time) on 13 May 1997. Broadly, it applies to you if you effectively had no interest in a dividend because you were under an obligation to make, or were likely to make, a related payment to another party for the dividend and you did not hold your shares 'at risk' for at least 45 days (90 days for certain preference shares).
When working out the number of days you held the shares 'at risk', do not count the day on which you acquired the shares and the day on which you disposed of the shares (or you entered into an arrangement to reduce the risk of making a loss on them).
A related payment includes you, or your associate, doing something under an arrangement that has the effect of passing the benefit of the dividend to someone else.
If either the holding period rule or related payments rule is likely to affect you, see You and your shares 2012 (NAT 2632).