Sources We Rely On

Figures stored with a source

73 figures are recorded in our data file, drawn from 9 agency documents. “Last checked” is the date we compared the figure with the page. Agencies sometimes revise a page after publishing, so if what you see there differs, let us know.

Rules, publications and forms our tools refer to

Beyond stored figures, calculators apply rules that agencies explain in their own publications. These are the ones we point to most often, grouped by topic.

Social Security

• How benefits are computed, with worked examples (Office of the Chief Actuary)
• Bend points for the benefit formula
• Contribution and benefit base
• Full retirement age by birth year
• SSA publication EN-05-10069 on earnings limits and examples
• SSI federal payment amounts
• Social Security Trustees Reports
• my Social Security account (your own earnings record)

Medicare

• Medicare costs overview
• When you can sign up
• Avoiding late-enrollment penalties
• Income-related monthly adjustment amount (IRMAA)
• Form SSA-44, request to reduce IRMAA after a life-changing event
• Extra Help with Part D costs
• Medigap (Medicare Supplement) basics
• Medicare Plan Finder

Federal taxes and retirement accounts

• Publication 915, Social Security and equivalent railroad retirement benefits
• Publication 590-B, distributions from IRAs
• Publication 505, tax withholding and estimated tax
• Publication 969, health savings accounts
• Form 5329, additional taxes on retirement plans
• Form W-4V, voluntary withholding request
• Form W-4R, withholding from retirement distributions

Medicaid

• Spousal impoverishment rules
• Informational Bulletin of April 27, 2026

How to read this page

A source here means the agency page we read, not an endorsement of us by that agency. For how a figure moves from these documents into a result, see how our calculators work.