How to Calculate Cost of Living Adjustments: Formula and 2026 Example

To calculate a cost of living adjustment, take the average Consumer Price Index for the third quarter of the current year, subtract the average for the third quarter of the last year a COLA took effect, divide by that base-period average, multiply by 100, and round to the nearest tenth of a percent. That is the formula the Social Security Administration uses, and it is the same subtract-divide-multiply structure the Bureau of Labor Statistics recommends for any contract that escalates with inflation.¹

The Formula in Five Steps

Every COLA calculation follows the same five moves. The only things that change are which index you use and which two periods you compare.

Step 1 — Average the comparison period. Add the CPI values for July, August, and September of the current year and divide by three.
Step 2 — Average the base period. Do the same for the third quarter of the last year a COLA took effect. In most years that is the prior year, but a zero-COLA year pushes the base back to the last year that produced an increase.²
Step 3 — Subtract. Comparison-period average minus base-period average. If the result is zero or negative, the COLA is zero; benefits never decrease because of deflation.²
Step 4 — Divide by the base. Difference ÷ base-period average. This gives you the raw ratio of price growth.
Step 5 — Convert and round. Multiply by 100 to get a percentage, then round to the nearest tenth of a percent. A result of 2.749% rounds down to 2.7%; 2.750% rounds up to 2.8%.

The rounding rule is small but consequential, because the rounded figure is what actually gets applied to millions of benefit checks.

Which Index to Use and Where to Find It

For Social Security, federal law requires the Consumer Price Index for Urban Wage Earners and Clerical Workers, abbreviated CPI-W.³ The CPI-W tracks spending patterns of households where more than half the income comes from clerical or wage-paying jobs, covering roughly 28% of the U.S. population. The broader CPI-U covers about 88% of the urban population, including retirees, the self-employed, and the unemployed, and is used for federal income tax bracket adjustments rather than Social Security.⁴

Both series are on the Bureau of Labor Statistics website under the Consumer Price Index databases.⁵ Always pull the unadjusted column. Seasonally adjusted figures smooth out predictable patterns like holiday spending, which makes them useful for economic analysis but unreliable for escalation because they get revised annually. BLS explicitly advises against using seasonally adjusted data for contract or benefit calculations.⁶

If you are calculating an adjustment under a private contract, lease, or alimony agreement, check which index the document names. Some contracts specify CPI-U or a regional CPI rather than CPI-W, and some use different months as the base and comparison periods. Using the wrong index or the wrong months is one of the most common errors, and it can produce a noticeably different percentage.

A Worked Example Using the 2026 COLA

Here is the calculation the Social Security Administration ran to produce the 2026 COLA of 2.8%.²

Average CPI-W for the third quarter of 2025 (comparison period): 317.265
Average CPI-W for the third quarter of 2024 (base period): 308.729
Subtract: 317.265 − 308.729 = 8.536
Divide by the base: 8.536 ÷ 308.729 = 0.02765
Multiply by 100: 2.765%
Round to the nearest tenth: 2.8%

Congress built the automatic-adjustment framework, and the zero-floor rule, into the 1972 Social Security Amendments; the first automatic COLA took effect in 1975.⁷

Applying the Percentage to Your Benefit

Once you have the percentage, turning it into dollars takes one multiplication. Convert the percent to a decimal, multiply your current monthly benefit by that decimal for the dollar increase, and add it back. Or do it in one step by multiplying your benefit by 1 plus the decimal.

For the average retired worker whose monthly Social Security benefit was $2,015 before the 2026 adjustment:⁸

Percent as decimal: 2.8% ÷ 100 = 0.028
Dollar increase: $2,015 × 0.028 = $56.42
New monthly benefit: $2,015 + $56.42 = $2,071.42

Your adjusted benefit becomes the baseline for the next year’s calculation, so COLA increases compound year over year rather than always applying to your original amount.

Supplemental Security Income uses a different rounding rule at the end. The COLA percentage is applied to the annual SSI amount, the result is divided by 12, and the monthly figure is rounded down to the next whole dollar rather than to the nearest cent. For 2026, that produces a maximum federal SSI payment of $994 per month for an eligible individual and $1,491 for an eligible couple.⁹

Using the Same Math for Other Benefits and Contracts

Several federal programs use the CPI-W result directly. VA disability compensation, dependency and indemnity compensation, and clothing allowances all take the same COLA percentage as Social Security, effective January 1. Military retirees under the Final Pay, High-36, and Blended Retirement System plans also receive the full CPI-W COLA. REDUX retirees get a reduced COLA, typically one percentage point below the standard rate but never below zero, with a one-time catch-up at age 62 that restores the cumulative difference before the reduced rate resumes.¹⁰

Federal civilian retirement follows two different rules. Civil Service Retirement System annuitants receive the full CPI increase starting the year after retirement. Federal Employees Retirement System annuitants generally do not receive a COLA until age 62, and the percentage is capped by a sliding formula:¹¹

CPI increase of 2% or less: FERS COLA equals the full CPI increase.
CPI increase between 2% and 3%: FERS COLA is capped at 2%.
CPI increase of 3% or more: FERS COLA equals the CPI increase minus 1 percentage point.

With the 2026 CPI-W increase at 2.8%, eligible FERS retirees received a 2% COLA rather than the full 2.8%.

SNAP adjusts differently. Its maximum allotments, income thresholds, and standard deductions change at the start of the federal fiscal year on October 1, using a methodology tied to the Thrifty Food Plan rather than the CPI-W, so the SNAP adjustment does not have to match the Social Security COLA.¹²

State and local public pensions vary widely. Some provide a fixed annual increase of 1% to 3%, some tie the adjustment to CPI with a cap, and others provide no automatic COLA. Check your pension administrator’s annual statement for the specific rule.

What the Calculation Doesn’t Tell You

The percentage you compute is the gross increase, not the net one you feel. Two other pieces of the picture routinely shrink it.

The first is Medicare. Most Part B premiums are deducted directly from Social Security checks, so a premium hike offsets part of the COLA. For 2026, the standard Part B premium rose to $202.90 per month, up $17.90 from $185.00 in 2025.¹³ For the average retiree, that $17.90 claimed roughly a third of the $56 monthly COLA increase, leaving a net of about $38. A federal “hold harmless” rule caps the Part B premium increase at your Social Security COLA dollar amount, so your check cannot shrink from one month to the next.¹⁴ The protection does not extend to high-income beneficiaries who pay income-related surcharges, and it does not extend to people new to Medicare. The Part B annual deductible, which rose to $283 for 2026 from $257, is not covered by hold-harmless at all.

The second is tax. A higher benefit is real income to the IRS. Once your combined income crosses federal thresholds, a larger share of Social Security becomes taxable, and a COLA bump can nudge you across that line or increase the taxable portion. The federal income tax brackets themselves are indexed for inflation using the Chained CPI-U rather than the CPI-W, so a COLA-only increase rarely pushes anyone into a higher bracket on its own. The more common trigger is a COLA combined with other income growth, such as a pension increase, required minimum distributions, or part-time wages.¹⁵ If a COLA raise changes your withholding needs, IRS Form W-4V is the form Social Security recipients use to adjust it.

1
Bureau of Labor Statistics. How to Use the CPI for Contract Escalation
2
Social Security Administration. Latest Cost-of-Living Adjustment
3
Office of the Law Revision Counsel. 42 USC 415 – Computation of Primary Insurance Amount
4
U.S. Bureau of Labor Statistics. Why Does BLS Provide Both the CPI-W and CPI-U?
5
U.S. Bureau of Labor Statistics. Consumer Price Index Data Databases
6
U.S. Bureau of Labor Statistics. Using Seasonally Adjusted and Unadjusted Data
7
Social Security Administration. Cost-of-Living Adjustment (COLA) Information
8
Social Security Administration. 2026 Cost-of-Living Adjustment (COLA) Fact Sheet
9
Social Security Administration. SSI Federal Payment Amounts for 2026
10
Military Compensation and Financial Readiness. Retired Pay
11
Office of Personnel Management. A Guide to Choosing Between FERS and CSRS
12
Food and Nutrition Service. SNAP Cost-of-Living Adjustment (COLA) Information
13
Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
14
Office of the Law Revision Counsel. 42 USC 1395r – Amount of Premiums for Individuals Enrolled Under Part B
15
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026