Sources
We use only the Social Security Administration, the Centers for Medicare & Medicaid Services, Medicare.gov, the IRS, and the law and regulations themselves. Each page lists its sources and the date we last checked them. Projections are labeled; we never post a guess as an official number.
IRMAA
Your tier comes from the official CMS table for the premium year, compared with your modified adjusted gross income from two years before. The lines are applied exactly as published: "less than or equal to" for the first tiers and "greater than or equal to" for the top one. Cents are dropped because the tax return uses whole dollars.
COLA
We apply the COLA to the benefit you enter and round down to the dollar. Social Security applies it to your base benefit before reductions and rounds to the dime first, so your notice can differ by about a dollar. The deposit is rounded down to the dollar after Medicare is taken out.
When to claim
Full retirement age by birth year; reductions of 5/9 of 1% a month for the first 36 months early and 5/12 of 1% beyond (20 CFR 404.410); delayed credits of 2/3 of 1% a month to 70 (20 CFR 404.313). Amounts are in today's dollars. Spousal and survivor benefits are left out.
Taxable Social Security
IRS Publication 915, Worksheet 1, line by line. Special cases that need other IRS worksheets are listed on the page.
Roth conversions
2026 federal brackets, standard deduction, extra deduction for 65 and older, and the senior deduction, applied to ordinary income. Taxable Social Security is recomputed with the conversion included. The Medicare effect uses the current IRMAA brackets as a warning; the brackets two years out will be adjusted for inflation. No state tax, itemized deductions or capital-gains rates.
Earnings test
The 2027 yearly limits and withholding ratios from Social Security. Whole monthly checks are counted from January, as Social Security usually withholds them. The first-year monthly rule isn't modeled.
Corrections
Found a mistake? Email hello@retirekept.com. We fix it and note the change.
Updated November 6, 2026.