The 2027 Social Security COLA Is Expected Oct. 14. Here's What September's Inflation Data Needs to Show

Social Security's 2027 raise is nearly locked in: two of the three months of inflation data that determine it are already published. The Social Security Administration (SSA) is expected to announce the 2027 cost-of-living adjustment (COLA) on Wednesday, Oct. 14, right after the Bureau of Labor Statistics (BLS) releases September inflation data at 8:30 a.m. ET.

Forecasts cluster in a tight range: about 3.4% to 3.6%, compared with 2.8% for 2026. If it lands there, it would be the largest COLA since 2023. Here's how the final number gets set, and why the headline raise isn't the whole story.

How the COLA formula works

The COLA is tied to a specific inflation index: the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W). It's a version of the CPI built around households that get more than half their income from clerical or hourly-wage jobs, a group that covers about 30% of the U.S. population. Retirees aren't its reference group, which has long been a point of debate.

The formula is mechanical:

1. Average the CPI-W for July, August and September of this year.
2. Compare that average with the same three-month average from last year (the last year a COLA took effect).
3. Round the percentage change to the nearest tenth of a percent.

For the 2027 COLA, the comparison point is the third-quarter 2025 average of 317.265, according to SSA.

July and August CPI-W: two of three months are in

Energy is a big part of the story. In the August CPI report, BLS said energy prices were up 16.3% from a year earlier and gasoline was up 27.4%, with gasoline alone accounting for more than a third of the month's overall increase. Higher oil prices tied to the conflict involving Iran have been a key driver this year.

What September needs to show

With July and August locked in, September's CPI-W reading decides the final number. Based on the published index values, here's roughly how it breaks down (our calculation; small rounding differences are possible):

In other words, a flat-to-slightly-higher September keeps the COLA around 3.4% to 3.5%, while another energy-driven jump could push it to 3.6% or more. Monthly inflation can surprise in either direction, so treat every forecast as an estimate until the official announcement.

Where the forecasters stand

• AARP: 3.6%
• The Senior Citizens League (TSCL): 3.5%, down from 3.6% in its July estimate
• Mary Johnson, independent Social Security analyst: 3.5%
• Committee for a Responsible Federal Budget (CRFB): 3.4%, as reported by CNBC on Sept. 11

What it could mean in dollars

SSA says the average retired-worker benefit was $2,071 a month in January 2026. Applied to that figure, a 3.4% to 3.6% COLA would add roughly $70 to $75 a month. Your increase depends on your own benefit amount, and SSA will publish updated averages with the announcement.

The Medicare Part B offset

For many retirees, the Medicare Part B premium is deducted directly from their Social Security check, so a premium increase eats into the COLA.

• 2026 standard Part B premium: $202.90 a month
• 2027 projection in the 2026 Medicare Trustees Report: $209.50, an increase of $6.60

That's a projection. The Centers for Medicare & Medicaid Services (CMS) usually announces the actual premium later in the fall, typically in November. Using the Trustees' figure, the average retiree would still keep most of a roughly $70-plus increase.

The hold-harmless rule, and who it doesn't cover

A provision called hold harmless generally prevents a Part B premium increase from shrinking a person's net Social Security payment, for most people whose premium is deducted from their benefit. But it doesn't apply to everyone. According to the Medicare Rights Center, people not protected include:

• New Medicare enrollees
• People who pay IRMAA, the income-related surcharge on Part B for higher earners
• People whose Part B premium isn't deducted from their Social Security benefit

What else gets announced the same day

Alongside the COLA, SSA typically updates several figures tied to wages rather than prices. For reference, here are the 2026 amounts:

• Maximum earnings subject to Social Security tax (taxable wage base): $184,500. The Social Security Trustees project $190,200 for 2027.
• Retirement earnings test (for people collecting benefits before full retirement age): $24,480 a year, with $1 withheld for every $2 earned above the limit.
• Earnings test in the year you reach full retirement age: $65,160, with $1 withheld for every $3 earned above the limit.
• Earnings needed for one work credit: $1,890.
• Maximum monthly benefit at full retirement age: $4,152.

Will a bigger COLA make more of your benefits taxable?

A larger COLA can also affect taxes. Up to 50% of benefits can become taxable once "provisional income" (roughly adjusted gross income plus half of Social Security benefits) passes $25,000 for single filers or $32,000 for joint filers, and up to 85% above $34,000 or $44,000, respectively. None of these thresholds are indexed to inflation. We covered that in more detail in July.

The new enhanced deduction for seniors, worth up to $6,000 per person age 65 and older for tax years 2025 through 2028 and phasing out above $75,000 of modified adjusted gross income ($150,000 for joint filers), can lower taxable income. It does not change the provisional-income formula itself. How any of this applies depends on your full tax picture, which is worth reviewing with a tax professional.

The takeaway

The 2027 COLA is largely determined by data already published. Forecasts point to roughly 3.4% to 3.6%, with September's inflation reading deciding the final tenth of a percent. SSA is expected to make it official Oct. 14. Medicare's 2027 premium, due later this fall, will determine how much of that raise actually reaches retirees' bank accounts.

This article is educational commentary on public economic data, not personalized financial, retirement or tax advice.