Most federal retirees will see their annuity benefits increase by 2 percent in January, the largest inflation-based increase since 2012 and an amount about in line with what current federal employees stand to receive as a pay raise.

The cost of living adjustment, or COLA, reflects the increase in a consumer price index measure from the third calendar quarter of one year to the next. The calculation was finalized Friday after taking into account inflation in September.

The impact on benefits will differ between the two main federal retirement systems. While more than nine-tenths of current federal employees are under the Federal Employees Retirement System — which generally covers those first hired after 1983 — two-thirds of the 2.1 million federal retirees draw benefits from the older Civil Service Retirement System.

The CSRS program provides for a full COLA adjustment to all retirees regardless of age. The average monthly annuity under that program is about $3,600, meaning that the increase will be worth about $72 monthly on average.

Those retired under CSRS do not receive Social Security benefits due to their federal service, although they may be eligible for Social Security benefits from other employment. However, in most cases, an offset would reduce the Social Security payments.

Under FERS, an inflation adjustment isn’t paid until age 62, except for those who retired due to disability or from certain occupations that require earlier retirement. The average monthly civil service benefit under FERS is about $1,400, yielding an average increase, for those eligible, of $28.

Those retired under FERS are eligible for Social Security benefits under standard rules and those receiving that benefit — which generally cannot begin earlier than age 62 — will see that payment boosted by 2 percent as well.

Both of the federal retirement programs increase benefits to survivors regardless of their age; there are about 530,000 of them, with average benefits of about $1,600 a month under CSRS and about $600 a month under FERS.

Federal employee and retiree organizations commonly bench mark the COLA figure against the average increase in premiums for the following year in the Federal Employees Health Benefits Program, which for 2018 will rise by 6.1 percent on average.

In the Blue Cross-Blue Shield standard option that is the most popular among retirees, for example, the increases per month will be $15.54 for self-only coverage, $36.92 for self plus one, and $38.39 for family coverage. However, premium rates and annual changes vary substantially among plans, and in an open season starting Nov. 13, retirees and other enrollees may change plans for 2018.

The COLA is also commonly compared with the pay raise for current employees, although the two are determined in different ways. While the COLA adjustment for retirees is set automatically by the inflation count, raises for current employees are decided in the annual federal budget process.

So far this year, Congress has been silent regarding a raise, following its practice of recent years of allowing a raise to be paid each January by default, as federal pay law provides if no number is enacted. President Trump has set the default raise at 1.9 percent.

Part of that raise would be set aside and parceled out in amounts that would vary by locality, resulting in raises that would vary from slightly below 1.9 percent to slightly above. Precise numbers would be set later in the year. However, if any other figure is enacted to law before the end of the year, that figure would prevail.