The carry forward rule is a provision that allows Members to contribute unused amounts as concessional contributions.
As of the 1st of July 2018 if your total superannuation balance is less than $500,000 you are able to add unused amounts to your original concessional contributions cap of $25,000.
As an example, say you contributed $17,500 in concessional contributions to your Fund in the 2019 Financial year, you will then be able to carry forward $7,500 into the 2020 Financial year. The total limit for your concessional contributions for the 2020 Financial year will now be $32,500. Any unused amounts from years after 1 July 2018 are available for five years carried forward. If they are not used in this 5 year time-frame they will expire.
The table below illustrates a Fund that would have more than the allowed amount to receive the carry forward rule, hence the Fund can only contribute $25,000 in concessional contributions.
The table below illustrates a Fund that would have an increasing amount in unused cap to receive the carry forward rule, hence the Fund can only contribute more in concessional contributions in further years within a five-year period.
The ATO have a full index of listings regarding the concessional contributions cap amount and unused amount. For more information please refer to the ATO website here.