Labor would introduce its changes to negative gearing and capital gains tax by January 1 next year if it wins the May election.

The negative gearing reforms won't apply to newly-built homes and existing investment properties, while the capital gains tax discount will be halved for investments entered into after January 1.

Shadow treasurer Chris Bowen said the property tax changes would raise $2.9 billion over the forward estimates, and save the budget $32 billion over a decade.

"If you already use negative gearing, nothing changes. It's not retrospective. And you can still use it for new houses," he said in a statement on Friday.