Calculator / Methodology

Methodology and limits

The government COLA calculation and the simpler benefit estimate used by this calculator.

Last checked Oct 14, 2026 · Published by Cornelia Cove LLC

1. Determine the COLA

SSA compares the current third-quarter average CPI-W with the third quarter of the last year in which a COLA became effective. For this determination, the comparison year is 2025. A positive increase is rounded to the nearest tenth of one percent; if there is no increase, or rounding produces zero, there is no COLA (SSA calculation rules).

COLA (%) = round to nearest 0.1 of
100 × (current Q3 CPI-W average ÷ base Q3 CPI-W average − 1)

CPI-W means the Consumer Price Index for Urban Wage Earners and Clerical Workers. We use the national all-items, not seasonally adjusted series CWUR0000SA0. The table shows the verified observations, rather than forecasts (SSA CPI-W table; BLS series CWUR0000SA0).

Sources: SSA calculation, SSA monthly table; 2026 values also checked against BLS series CWUR0000SA0. Checked Oct 14, 2026.

For the 2027 payment-year example, the averages are (316.349 + 317.306 + 318.139) ÷ 3 = 317.265, and (327.104 + 328.481 + 330.654) ÷ 3 = 328.746, each displayed to three decimals. Using those displayed averages gives (328.746 ÷ 317.265 − 1) × 100 ≈ 3.6187%, rounded to 3.6%. The calculator retains full precision in its averages; both routes yield 3.6% (SSA worked calculation).

The official default is SSA’s announced 3.6%, rather than a forecast. It is effective for December 2026 benefits, paid in January 2027 (SSA 2027 information).

2. Estimate the gross benefit

new gross = floor(current gross × (1 + COLA ÷ 100))
monthly increase = new gross − current gross
annual increase = monthly increase × 12

Here, floor means discard the fractional dollar. For an illustrative $2,000 current monthly benefit and 3.6% COLA, floor($2,000 × 1.036) = $2,072. The estimated increase is $72 a month, or $864 over 12 equal payments. This is calculator arithmetic, not a quoted SSA benefit award.

3. Subtract assumed Part B premiums

current net estimate = current gross − 2026 Part B premium
new net estimate = new gross − assumed 2027 Part B premium
net change = new net estimate − current net estimate

Both deductions are zero when you select “No” for Part B deducted from your check. When you select “Yes,” the current deduction is fixed at the 2026 standard premium, $202.90 (CMS); only the assumed 2027 premium is editable.

The 2026 standard premium is $202.90 (CMS). No published CMS 2027 standard premium was found as of Oct 14, 2026; Medicare.gov still lists 2026 costs. The default is a 2026-based assumption, not an official 2027 amount. Change it to test a different premium.

With the $2,000 example and $202.90 assumed in both years, the displayed net estimates are $1,797.10 and $1,869.10, a $72 difference. These cents reflect this tool’s subtraction order. SSA subtracts an offset such as the Part B premium first and then truncates the result to the next lower dollar (SSA explanation), so an actual payment would not end in cents.

What the tool leaves out

• PIA and payment rounding. SSA applies the COLA to the primary insurance amount (PIA), truncates to a lower dime, applies relevant retirement factors and offsets, and truncates the resulting payment to a lower whole dollar. Applying a percentage directly to an already rounded gross benefit and then subtracting a premium cannot reproduce that sequence exactly (SSA explanation; SSA rounding policy).
• Part B hold harmless. For qualifying beneficiaries, this protection limits a premium increase that would otherwise reduce the benefit payment. It has entitlement and deduction conditions and does not apply to income-related premiums; state Medicaid premium payments are also excluded. The calculator simply subtracts your assumption and does not assess this protection (Social Security Act §1839(f); SSA operational rules).
• IRMAA and other Medicare charges. Income-related monthly adjustment amounts can increase Part B premiums; Part D premiums vary. The tool does not calculate these, late-enrollment penalties or other plan charges (Medicare cost guidance).
• Tax withholding. Social Security benefits can have voluntary federal income tax withholding. No tax is subtracted here (IRS Form W-4V guidance).
• SSI versus Social Security insurance benefits. This estimates a Social Security (OASDI) benefit, not an SSI award. SSI amounts depend on income, living arrangements and possible state supplements; an identical COLA percentage does not make the programs’ payment calculations interchangeable (SSA SSI guidance).

The annual figure assumes 12 unchanged monthly increases. It does not model changes during the year or establish an entitlement. For the final amount, consult your SSA COLA notice (SSA notice information).