The government claims that all couples who own their home with additional assets of up to $450,000 will get a higher pension, but an analysis conducted by Industry Super for the Senate inquiry into the changes finds that some couples will be $2900 worse off than the government claims.

The Coalition and The Greens combined on Thursday to force the inquiry to report on Monday, allowing a Senate vote as soon as this week. The accelerated timetable means the inquiry will be unable to hold hearings.

The changes lift the assets-test free limit for homeowner couples from $286,500 to $375,000 but withdraw the pension much faster than before, by $3 for every $1000 of assets over the limit rather than $1.50.

A supplementary submission to the inquiry by Industry Super says the tables presented with the budget focus on the changes to the pension assets test without acknowledging that access to the pension is also governed by an income test which 'deems' income from assets. The more restrictive test prevails.

Recalculating the government's figures to include both tests, Industry Super finds a homeowner couple with assets of $375,000 would be no better off under the changes, not the $2984 better off as claimed by the government.

"The gains for pensioners with lower levels of assets are either considerably overestimated or non-existent," the submission says.

It also takes issue with two assumptions unlikely to borne out by reality.

The department of social security uses life expectancy estimates up to 11 years lower than those used in the government's intergenerational report. The estimates are so-called 'period' estimates prepared by the Bureau of Statistics without taking into account likely advances in longevity. The treasury prefers the 'cohort method' which "takes a better account of increasing life expectancy trends over time". The effect of the department's choice is to make it look as if the assets of retirees who miss out on the pension will last for more of their life than they will.

It also assumes rates of return on assets well above those used by other agencies and points to the gain in the sharemarket index of 12.7 per cent in the past year without acknowledging that it was unusual.

Industry Super asks the Senate to hold a proper inquiry before voting, pointing out that the changes are not due to take effect until 2017.