The Morrison government's promised $1080 low and middle income tax boost to 4.5 million Australian taxpayers which would lift the economy has turned into a $420 bump barely noticed by the nation's shopkeepers.

Australian Tax Office figures show the average tax refund received by those who rushed to get the tax offset announced in this year's budget have received far less than expected.

In the April budget, Treasurer Josh Frydenberg unveiled a doubling of the low and middle income tax offset which he said would deliver up to $1080 to single earners and up to $2160 for dual wage families.

Hefty tax refunds have fallen well short of budget expectations as a record number of people do their own tax. Credit:istock

He said 10 million taxpayers would get some of the offset with 4.5 million getting the full amount, which the Treasurer predicted would flow quickly into the economy.