The average annuity is paying £2,058 less income over retirement than it did before Chancellor George Osborne's March Budget.
The average annuity rate for the three months to March 2014 was 6.34%, according to analysis from MGM Advantage, giving customers an annual income of £3,172 (based on converting a pension worth £50,000).
However, during the quarter ending September 2014, the rate fell to 6.14%, cutting the annual income by over 2% to £3,074.
Over the average lifespan an annuity pays out for, the lower rate would see today's annuitants receive almost £100 less a year than those who locked in their money during the three months to March.
Enhanced annuity customers - those who have shorter life expectancy than standard annuity customers - fared worse over the six-month period, with their income reducing by 3.5%.
Nevertheless, enhanced annuity customers secured 20% more annual income when arranging their annuities in the three months to September than standard annuity customers. They stood to receive income of £3,349 a year, compared to the £2,799 income stream fixed by standard annuity customers.
"Annuity rates have tumbled," said Aston Goodey, sales and distribution director at MGM Advantage. He put the reduction down to "the yields available on gilts and other fixed interest investments, as well as the uncertainty remaining in the market following the Budget".
He added: "Unfortunately, this all means people who buy an annuity today will receive less income over retirement than those people who purchased earlier in the year. The difference in rate can make a significant difference in the amount of income over an average retirement."
Goodey urged anyone considering an annuity to shop around and "ensure the company providing the annuity is considering their individual circumstances when calculating the annuity rate".
This means customers should make sure the company has all relevant information, which includes age and occupation, where they live, as well as a picture of their overall health and lifestyle.
Goodey also warned that annuity rates are not set to rise in the near future: "The outlook for annuity rates remains unpredictable. Any improvements in interest rates and the yields available on gilts should help move rates up. However, the market is talking about the middle of next year before we are likely to see any increase in interest rates."
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