The 2027 Social Security Raise Comes Out of One Number Due October 14

Every autumn the size of next year's Social Security increase is treated as a forecast until, quite suddenly, it is arithmetic. The adjustment is not set by a vote or a judgement call. It falls out of a formula with one missing input, and this year that input is the September Consumer Price Index, scheduled for 8:30 a.m. Eastern on October 14, 2026.

The formula

The index used is not the headline CPI most people see quoted. It is the Consumer Price Index for Urban Wage Earners and Clerical Workers, the CPI-W. The calculation takes the average CPI-W across July, August and September, and compares it with the average across the same three months of the last year in which an adjustment was determined. The percentage difference, rounded to the nearest tenth of one percent, is the adjustment.

The most recent calculation shows the mechanics plainly. The third-quarter 2025 CPI-W average was 317.265. The third-quarter 2024 average was 308.729. The difference, 8.536, divided by 308.729, is 2.8 percent after rounding. That is the figure now in benefit cheques.

Why the quarter matters more than the month

Because the comparison runs on a three-month average rather than a single month, no one month can move the result by much on its own. July and August 2026 are already measured and published. Only September is outstanding. Whatever that reading is, it enters the average as one third of one side of a ratio — which is why the range of plausible outcomes narrows sharply once the August figure is in hand, and closes entirely on October 14.

When it applies, and to which cheque

The adjustment does not start with the calendar year. It applies to benefits for December, which are payable in January. The 2.8 percent increase announced on October 24, 2025 applied to December 2025 benefits, paid in January 2026. The same pattern governs whatever figure emerges this month.

The Social Security Administration's own statement is that it will announce the next adjustment in October 2026. It has not published a date. Last year's announcement came on October 24, well after the usual mid-October timing, which is worth bearing in mind for anyone expecting the figure the same morning the CPI lands.

The rounding rule is not a rounding error

Rounding to the nearest tenth of a percentage point means the published adjustment can differ from the raw calculation by up to five hundredths of a percentage point in either direction. On a $2,000 monthly benefit that is about a dollar a month. It is small, but it is the reason two people computing the figure from the same index values can disagree before the official number is out.

What to watch

Two publications settle this, in order. The CPI release on October 14 supplies the last number. The Social Security Administration's announcement, some time in October, applies the formula to it. Nothing between those two events changes the answer.