The size of the Morrison government's first round of tax cuts has fallen well short of expectations, as workers shun accountants and fail to make deductions, casting doubt on their impact on Australia's sluggish economy.

Ahead of Tuesday's Reserve Bank board meeting at which official interest rates are expected to be cut to a fresh record low of 0.75 per cent, The Sydney Morning Herald and The Age can reveal that despite the new low and middle-income tax offset that promised to pump up to $1080 into the pockets of cash-strapped households, there has only been a modest lift in refunds.

The average refund sent to more than 6.6 million Australians is now $2638, Australian Tax Office data shows, just $250 more than the average refund recorded through the first four months of the 2018-19 financial year.

Since July 1 there has been a 13 per cent jump in tax returns lodged with the ATO, with a surge in the number of taxpayers lodging returns themselves as they attempt to get their hands on the low and middle-income tax offset.