Methodology
Every formula on this site is checked against a named primary source before it ships. This page lists all of them — the full reference apparatus behind the calculator library, not a curated selection. Where a government body defines a figure, we use that body and nothing else.
Last full library audit: August 24, 2026. Rate defaults are reviewed monthly; tax figures are updated each November when the IRS, SSA and FHFA publish the following year's numbers.
Anything that is legally defined — a tax bracket, a contribution limit, an RMD divisor, an insurance premium rate — comes from the body that sets it. No aggregator sits between us and the rule.
Current-condition figures — average mortgage rates, auto loan APR by credit tier, typical home values — come from market data publishers and load as editable defaults. They shape the first number you see, never the arithmetic.
Our verification file forbids attaching an authority to a calculator without a checked URL. Tools whose maths is a standard accounting identity carry no citation at all rather than borrow one that does not apply.
The wider process — who reviews formulas, how corrections are handled, and what we will not publish — is set out in our editorial policy.
Statute, regulation, and official statistics. These are the bodies that actually set the numbers — tax brackets, contribution limits, benefit formulas, published rates. Where a federal source exists for a figure, we use it and nothing else.
Federal tax brackets and standard deductions (Rev. Proc. 2025-32, as amended by the One Big Beautiful Bill), retirement contribution and catch-up limits, Publication 590-A and 590-B for IRA contributions, distributions and the Uniform Lifetime and Single Life expectancy tables behind every RMD calculation, Publication 505 for withholding and estimated tax, Publication 936 for the mortgage interest deduction, Publication 969 for HSA rules, Publication 527 for rental property depreciation, Publication 575 for pension and annuity income, Topic 409 for capital gains treatment, Rev. Rul. 59-60 for closely held business valuation, and Fact Sheet FS-2008-25 on S corporation officer compensation.
Amortization methodology for every mortgage, auto and personal loan tool; the Regulation Z definition of APR that our fee-inclusive loan comparison solves for; credit card interest accrual and minimum-payment mechanics; HELOC draw and repayment period behaviour; the debt-to-income thresholds used in affordability tools; and the Loan Estimate structure our closing cost estimator mirrors.
Cost-of-living adjustment history, the annual taxable wage base used in payroll and self-employment tax, full retirement age and early-claiming reduction factors, and the Office of the Chief Actuary Period Life Table that drives our annuity payout mortality model.
H.15 Selected Interest Rates for CD and deposit rate defaults, the G.19 Consumer Credit release for average credit card APR, the Z.1 Financial Accounts for household balance sheet context, and the Survey of Consumer Finances, which supplies the net worth percentile benchmarks and the household balance-sheet comparisons.
CPI-U, U.S. city average, all items — the series behind every inflation adjustment, real-return calculation and historical purchasing power figure on the site. Consumer Expenditure Survey data backs the category benchmarks in budgeting tools, and Employer Costs for Employee Compensation supplies the benefit load percentages in the employee cost calculator.
7(a) loan structure and terms, and the small business financial management guidance behind our break-even, cash flow and employee cost tools.
Repayment plan definitions and formulas — Standard, Graduated, Extended and the income-driven plans — plus consolidation rules and forgiveness eligibility criteria used across the student loan suite.
FHA loan limits by county, upfront and annual mortgage insurance premium rates, and the FHA qualification ratios in our FHA calculator.
The investor bulletin on fees and expenses that underpins our expense-ratio drag modelling, and disclosure standards referenced in investment explainer content.
Selling Guide underwriting standards — qualifying ratios, reserve requirements and rental income treatment — used in affordability, DSCR and house-hacking tools.
Investor education material on compounding, fee impact and margin, referenced in investing explainer content.
CPIAUCSL for the inflation series and WPRIME for the prime rate, used as the machine-readable mirror of the primary BLS and Federal Reserve releases.
VA loan entitlement rules and the funding fee schedule by service category, down payment and first-versus-subsequent use.
The compound interest methodology our savings, SIP, dollar-cost-averaging and investment growth calculators are verified against.
Deposit insurance limits and national deposit rate context in CD and savings account content.
The Primary Mortgage Market Survey, which sets the 30-year and 15-year rate defaults shown when a mortgage calculator loads. Reviewed monthly.
American Community Survey income and housing cost data used in the cost-of-living and affordability datasets.
Credit reporting rights and debt collection rules in credit-related explainer content.
Treasury yield curve rates and federal tax administration references.
Savings bond and Treasury security terms, rates and redemption rules.
High-deductible health plan definitions that determine HSA eligibility.
Final rules and notices for figures published by regulation rather than in a guide.
Statutory text and nonpartisan CRS analysis for recently changed tax and retirement law.
Maximum monthly guarantee tables by age and annuity form, set annually under ERISA — the ceiling on what a terminated private pension can actually pay. Drives the pension value calculator.
Annual conforming loan limits, including high-cost area limits.
Credit union share insurance limits and published loan rate comparisons.
Employer plan fiduciary rules and wage and hour standards in payroll cost tools.
Rural Development loan eligibility and guarantee fees, and the Food Plans cost estimates used as grocery benchmarks.
The federally mandated free credit report service, referenced in credit improvement guidance.
The Comptroller's Handbook on commercial lending, which documents the 365/360 interest accrual convention used by banks — a method that produces more interest than a borrower usually expects and has been repeatedly litigated.
Contribution limits, agency matching schedule and fund structure for the federal employee retirement plan.
FERS and CSRS annuity computation rules, creditable service definitions and eligibility ages for federal employees.
Fair Market Rents by metro area and county, published annually by law — the federal benchmark for what a standard-quality rental costs, used in rent increase analysis.
Regional Price Parities by state and metro area — the index behind every city-to-city cost of living comparison.
Household Debt and Credit Report, used for balance and delinquency context.
The long-run CPI series extending inflation comparisons back to 1800.
Premium and enrolment rules in retirement healthcare cost estimates.
Federal poverty guidelines, used as thresholds in income-driven repayment calculations.
Federal tax deposit scheduling referenced in quarterly estimated tax guidance.
Regulation text, including Regulation Z, where the exact wording governs a calculation.
Annotated Internal Revenue Code sections where the statute itself is the clearest reference.
Bankruptcy means test income standards in debt relief comparison content.
The VIN decoder that reports final assembly plant — the test for whether a vehicle qualifies for the car loan interest deduction.
Registration and disclosure standards referenced in investment risk content.
Equivalent authorities for our Canadian tools and the Canada affordability dataset — CRA rules, CMHC insurance premiums, Bank of Canada rates, Statistics Canada series.
Canada Revenue Agency federal and provincial tax brackets, RRSP and TFSA contribution room rules, CPP and OAS benefit formulas, and the Home Buyers' Plan withdrawal limits.
Mortgage loan insurance premium rates by loan-to-value band, minimum down payment rules, and the amortization limits that constrain Canadian mortgage calculations.
Canadian mortgage payment mechanics, including the semi-annual compounding convention that makes Canadian amortization differ from U.S. amortization.
Policy interest rate, the Canadian CPI series, and the inflation calculator baseline.
Household income, spending and shelter cost tables behind the Canadian provinces affordability dataset.
Guideline B-20 residential mortgage underwriting, including the minimum qualifying rate — the Canadian mortgage stress test.
Québec provincial tax brackets, which are administered separately from CRA.
Ontario land transfer tax rates and first-time buyer rebate thresholds.
Duty and import cost references in cross-border cost comparisons.
Municipal property tax mill rate for Yukon, where no territorial aggregate is published.
Where no government body defines a method, the profession does. Accounting identities, valuation conventions, and appraisal standards come from the organisations that publish them.
State-by-state income tax bracket compilations and effective property tax rates by county — figures each state publishes separately and no federal body aggregates.
Practice standards referenced in retirement planning methodology.
The AAII Journal publication of the Trinity Study — the withdrawal rate research our safe withdrawal rate, FIRE and retirement drawdown tools are verified against.
Accounting Standards Codification definitions for revenue, EBITDA components and lease treatment in business valuation tools.
Market Pulse survey multiples used as business valuation reference ranges.
MLS Home Price Index benchmark prices by province.
The multi-state rate and boundary tables maintained under the Streamlined Sales and Use Tax Agreement — the only body that publishes sales tax rates across member states in one place.
Valuation and attestation standards referenced in business tool methodology.
Global Investment Performance Standards for return calculation conventions.
Income capitalisation approach definitions behind cap rate methodology.
Existing home sales and median price series for market context.
Property management fee conventions used as rental analysis defaults.
Construction cost breakdowns in build-versus-buy content.
Filing statistics and process detail in debt relief comparisons.
Debt management plan structure and typical terms.
Bengen's portfolio success rate research — the origin of the 4% rule and the basis for our withdrawal rate ranges.
Peer-reviewed and institutional research behind the models that have no statutory definition — safe withdrawal rates, equity risk premiums, wealth distribution.
Global wealth distribution percentiles behind the international net worth comparison.
Equity risk premiums, industry cost of capital and EBITDA multiples by sector — the standard academic reference for valuation inputs.
Employer health benefits survey premiums in retirement and employee cost estimates.
Registered Statistics Canada data tables cited by permanent DOI.
Purchasing power parity conversion factors for international comparisons.
Residential property price statistics for cross-country housing context.
Distributional analysis of tax provisions in explainer content.
Long-run historical price and wage series for pre-1913 inflation comparisons.
Average student debt at graduation by state, used as calculator defaults.
State tax burden rankings in relocation comparison content.
Long-run return series and annuity pricing published by firms with the data to produce them. Used for historical context and defaults, never for rules.
Long-run asset class return series and the portfolio allocation models referenced in stock-and-bond split guidance.
S&P 500 historical average return series and retirement savings benchmark multiples.
Annual retirement income research updating safe withdrawal rate estimates against current valuations and yields.
S&P 500 index history and the Case-Shiller Home Price Index.
Global Wealth Report distribution data for international net worth percentiles.
Current market annuity quotes, used to sanity-check our actuarial payout model against real pricing.
Current-condition figures that no government publishes quickly enough — house price indices, average loan rates by credit tier, cap rate surveys. Used for defaults you can change, not for results.
State of the Automotive Finance Market — average auto loan APR by credit score band, and average balances by loan type. These set the rate defaults in auto tools.
Average personal loan rate surveys by credit tier, used as calculator defaults.
Average homeowners insurance premium by state in the affordability dataset.
The Zillow Home Value Index by state — the typical home value series behind the affordability index.
US Cap Rate Survey, used as the reference range in cap rate analysis.
Quarterly average new and used vehicle transaction prices and loan terms.
Aggregated Canadian land transfer tax and property tax rates by municipality, pending replacement with provincial primary sources.
Canadian property tax rate comparison by province, pending replacement with provincial primary sources.
Home Flipping Report gross margin and holding period benchmarks.
Shiller CAPE ratio series for valuation context in return assumptions.
Gross rental yield benchmarks by country.
Canadian mortgage market rate reporting.
Cited only where a practitioner published original analysis that became the reference implementation for a method. Never cited for a figure a primary source already carries.
The community wiki's documented three-fund and variable withdrawal methodologies, cited where it is the clearest public write-up of a method.
Michael Kitces' original analysis on Roth conversion sequencing and withdrawal ordering — practitioner research with no primary-source equivalent.
The BRRRR method definition and standard operating expense assumptions.
The Safe Withdrawal Rate Series — the most extensive public sequence-of-returns analysis, cited alongside the Trinity Study.
The savings-rate-to-retirement-date relationship popularised in FIRE planning.
Coast FIRE and Barista FIRE definitions as used in the FIRE calculator family.
Wade Pfau's work on withdrawal strategies and annuity integration.
Terminology definitions in business valuation content.
Historical market return context in investing explainer content.
Fetched at request time rather than stored, so the figure you see is the figure published now. Exchange rates only.
Current foreign exchange reference rates, fetched server-side at request time. Nothing is stored and no request is attributed to you.
Historical exchange rate series published by the European Central Bank, used for the currency trend chart.
Tax law changes, agencies restructure their sites, and published rates move. If a figure here looks stale or a formula does not match the source it cites, tell us and we will check it against the primary document and correct it. Include the calculator name and the figure you are questioning.
Report a correctionOrganisation names are used to identify the sources of the data and methods behind our calculators. The identifying marks shown above are our own typographic labels, not the logos or seals of the organisations named. Listing a source does not imply that organisation endorses, sponsors, reviews or is affiliated with We Are Calculator. We Are Calculator provides estimates for informational purposes only and is not financial, tax or legal advice — see our disclaimer.
