When the Reserve Bank slashed the official cash rate by 0.25 per cent last week, Australia's big four banks followed suit. However, almost half of the home loan market has yet to announce interest rate cuts, and the big four banks are set to pocket $21 million from the delay.

"That means they'll squeeze an estimated $1.25 million from mortgage customers each day they hold off cutting rates," said Bessie Hassan, Finder.com.au money expert. "Borrowers are not getting the full savings, they have to wait before they can benefit from that rate cut."

The Australian Military Bank plans to wait eight weeks to honor the rate cut while ME Bank announced a rate cut of just 0.05 per cent.

Among the big four banks, NAB was the first one to announce that it would cut its standard variable home loan by the full 0.25 per cent within 10 minutes of RBA's move. It will come into effect next Monday, earning the bank $3 million in repayments.

Both Westpac and Commonwealth Bank quickly followed RBA's lead and declared a full rate cut, but each of them will earn $8 million before borrowers see any relief as Westpac will wait 20 days to pass on the cut while Commonwealth Bank will wait 17 days.

ANZ will be the fastest to make a change, but it will only reduce its rate by 19 basis points, hence making an extra $2 million.

Economists are expecting another rate cut for August following the RBA's lower inflation forecast.