Because she supported passage of congressional pension changes that took effect in 1987, Boxer's office said, her pension would be $40,000 less than one she could have chosen.
"Senator Boxer voted for these reforms and she felt it was the right thing to do to live by them," said spokesman Zachary Coile.
And Boxer's pension will probably be even less than $86,000, her office said, because of survivor benefits that will go to her family.
Her office declined to discuss the specifics of those.
A principal driver behind her benefit is her tenure on Capitol Hill. She was first elected to the House in 1982, and then won her Senate seat in 1992, giving her 30 years in office.
Congressional pensions also depend on the three highest years of pay. Although congressional pay is $174,000, lawmakers have not raised their salaries since the financial crisis of 2008.
Political observers say it is easy to see why Boxer would want to clarify the NTU estimate.
"Legislators don't have very high standing as it is, and so the idea of outrageous pensions is another stick to beat them with," said Shaun Bowler, political scientist at the University of California at Riverside.
Members of Congress have the option of signing up for both pensions and 401(k)-type options. Pensions are known as defined-benefit plans, while a 401(k), or "thrift savings plan" as Congress calls it, is a defined-contribution plan.
Even $86,000 is "double the salary of the average American worker," said Cal Jillson, congressional expert at Southern Methodist University.
The Employee Benefits Research Institute says 31 percent of American private-sector workers have only a defined-contribution plan. And only 11 percent have both pensions and 401(k)-type plans. Less than 5 percent have a defined-benefit plan only.
"Few 401(k)s replace half the salary of an American worker, even at the professional level," Jillson added.
NTU estimated Sen. Dianne Feinstein, D-San Francisco, would have a $53,000 annual pension if she retired at the end of this year. She is running for re-election, however.
Feinstein's office declined comment.
Because Boxer was elected before 1987 changes in the congressional pension system, she had the choice of staying in the federal Civil Service Retirement System or opting for a new Federal Employees Retirement System.
NTU made its estimation assuming she had stayed in the civil service plan, which had the more generous pension benefit.
It also projected a $125,000 pension for Rep. Jerry Lewis, R-Redlands, who is retiring in January after 34 years on Capitol Hill.
Lewis' office did not dispute the figure and confirmed that he remained in the civil service plan through his career.
"Pension issues are a new flashpoint, especially government pensions for a whole range of reasons," said Bowler, the UC-Riverside professor.
"Times are tough for a lot of people who have gone through job loss and house loss and who are hearing yet again about how government spending on services need to cut back and so on."
Congressional experts also say many myths about lawmakers and their benefits continue, such as they don't have to pay into their pensions or they don't have to pay Social Security taxes.
The requirement that they pay Social Security taxes was not put into effect until 1984, according to the Congressional Research Service.
And congressional retirement benefits have a long history of controversy.
Civil service retirement benefits were first extended to lawmakers in January 1942 but were repealed "just two months later in response to adverse public opinion," a Congressional Research Service report says.
In 1946, the report adds, Congress again extended civil service retirement benefits to itself with higher contribution rates and higher benefits than those of other federal employees.
A Senate report accompanying the legislation that year said:
"(Retirement benefits) would contribute to independence of thought and action, (be) an inducement for retirement for those of retiring age or with other infirmities, (and) bring into the legislative service a larger number of younger Members with fresh energy and new viewpoints concerning the economic, social, and political problems of the Nation."
Contact Paul C. Barton at
Retirement options available to members of Congress@
Under the Civil Service Retirement System for members elected before 1984:@
-- Retirement with an immediate, full pension: Members aged 60 or older with 10 years of service in Congress, or aged 62 with five years of civilian federal service, including service in Congress.
-- Retirement with an immediate, reduced pension: Members aged 55 to 59 with at least 30 years of service. It is also allowed if a member left for a reason other than resignation or expulsion after having completed 25 years of service, or after reaching the age of 50 and with 20 years of service, or after having served in nine Congresses.
-- Retirement with a deferred, full pension:@ For members leaving before reaching the minimum age required to receive an immediate, unreduced pension and delays receipt until reaching the age at which full benefits are paid. A full pension can be taken at 62 if the member had five through nine years of federal service, or at the age of 60 if
-- Retirement with a deferred, reduced pension: Members who reach 50 and have at least 20 years of federal service, including at least 10 years as a member of Congress.|
Under the Federal Employees Retirement System for members elected in or after 1984:@
--Retirement with an immediate, full pension: Members aged 62 or older with at least five years of federal service; aged 50 or older with at least 20 years of service; and at any age to those with at least 25 years of service.
-- Retirement with an immediate, reduced pension: Available at 55 to those born before 1948 with at least 10 years of service. The minimum age increases to 56 for members born from 1953 through 1964 and to 57 for those born in 1970 or later.
-- Retirement with a deferred, full pension: Available at 62 to those with at least five years of federal service.
-- Retirement with a deferred, reduced pension: Available at the minimum retirement age of 55 to 57 (depending on year of birth) to a former member who has completed at least 10 years of federal service. The pension annuity is permanently reduced if it begins before the age of 62.
Source: Congressional Research Service