More than 600,000 retirees will know within a week by how much their fortnightly pension payment will be boosted as the government prepares to debate at least three changes to the welfare system after being savaged by seniors.

Prime Minister Scott Morrison's expenditure review committee will consider how to minimise the budget impact of changes to the deeming rate for pensioners, while acknowledging many are feeling short-changed because of the government's failure to match interest rate cuts.

The government assesses income from financial investments, such as term deposits, and includes them in the pension income test when they are assessing payments.

The government assumes a rate of return on these investments which is described as the deeming rate. Currently, the deeming rate for singles is 3.25 per cent for assets over $51,200 and 1.75 per cent for those under that level.