More than a million woman aged 60 to 62 have lost an average of £32 a week as a result of increases to the state pension age.
A report from the Institute of Fiscal Studies (IFS) says 1.1 million women over 60 who would have received a pension before 2010 are now having to wait longer to qualify.
As a result, rates of "absolute poverty" among the group, where incomes are below 60 per cent of the median, have risen, says the BBC.
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However, adds the IFS, the government's finances are better off to the tune of £5.1bn a year.
Until 2010, women were able to receive a state pension at 60. However, the coalition government that year introduced a programme of staggered changes to equalise the pension age at 65 by 2020. So far, women now qualify at the age 63.
That has meant those aged 60 to 62 have lost around £82 a week, only partially offset by the additional earnings they receive to leave them £50 a week worse off, says the Financial Times.
Changes in the income of a partner mean the overall household income level is down by a net average of £32 a week.
Despite the changes and the rise in poverty rates, the IFS said there had been no material change in the number of women experiencing "material deprivation", where they cannot afford a range of important items.
Pensions are the largest part of the welfare budget, accounting for more than £100bn a year after consistent increases in life expectancy.
The government borrowed £46bn to cover a shortfall of tax receipts against spending last year.
In addition to the £5.1bn gained from the pension reform - of which £900m is additional employment taxation - further changes to the pension age in the next 30 years will save the state an estimated £74bn.
The government said its pensions policy was "fair and sustainable".
