Methodology & Data Sources
ClearFigure is built on a simple principle: every number we show you must be traceable to an authoritative source. This page explains where our data comes from, how we verify it, and how we keep it current.
Our Accuracy Standards
We only publish calculators where the formula is deterministic and verifiable against a primary source — an IRS publication, a mathematical law, or official government data. We do not publish “estimate” tools where we can't show exactly how the answer was derived.
Every calculator on ClearFigure meets these requirements:
- Cited source: The specific IRS publication, FRED series ID, or BLS series that provides the data is identified on every page.
- Visible formula: The methodology section shows the exact mathematical formula used, with variable definitions.
- Last updated date: Every page displays when the data was last verified or when the live API was last fetched.
- Automated tests: Tax calculators are backed by a suite of hand-calculated test cases that verify the output against known-correct results. Currently 36 tests across federal income tax and self-employment tax.
- Cross-validation: Federal tax brackets are verified across three independent sources: the IRS Revenue Procedure, PSLmodels/Tax-Calculator, and the Tax Foundation.
Data Sources
Federal income tax brackets, standard deductions, capital gains rates, and other tax parameters. Published annually by the Internal Revenue Service.
- Examples:
- Rev. Proc. 2025-32 (2026 brackets), Rev. Proc. 2024-40 (2025 brackets)
- Update frequency:
- Annual (published October/November for following tax year)
- Used by:
- Federal Income Tax Calculator, Self-Employment Tax Calculator
Open-source structured tax parameter data maintained by the Policy Simulation Library. Contains 200+ tax variables in machine-readable JSON, indexed by year. Used by academic researchers and policy analysts.
- Examples:
- policy_current_law.json — all federal tax parameters 2013–2035
- Update frequency:
- Updated within days of IRS Revenue Procedure publication
- Used by:
- Cross-validation of federal bracket data
Federal Reserve Economic Data — the most comprehensive free source of US economic data. Provides real-time financial rates from authoritative sources including Freddie Mac and the Federal Reserve itself.
- Examples:
- MORTGAGE30US (30-year mortgage rate), MORTGAGE15US (15-year), DGS10 (10-year Treasury yield)
- Update frequency:
- Mortgage rates: weekly (Thursday). Treasury yields: daily.
- Used by:
- Mortgage Calculator (live rates via ISR)
Official CPI-U (Consumer Price Index for All Urban Consumers) data used to measure inflation. Series CUUR0000SA0, not seasonally adjusted, base period 1982–84 = 100.
- Examples:
- Annual average CPI 1913–2025 (113 years of data)
- Update frequency:
- Monthly (annual averages used in our calculator)
- Used by:
- Inflation / Purchasing Power Calculator
Official I Bond interest rates published by the Department of the Treasury. No authentication required. Returns fixed rate, inflation rate, and composite rate for all I Bonds since 1998.
- Examples:
- I Bonds Interest Rates dataset — semi-annual rate announcements
- Update frequency:
- Semi-annual (May 1 and November 1)
- Used by:
- I Bond Calculator (live rates via ISR)
Official FICA tax rates and Social Security wage base. Published at ssa.gov. Wage base is updated annually; FICA rates have been unchanged since 1990.
- Examples:
- 2026 SS wage base: $184,500. FICA rates: 6.2% SS + 1.45% Medicare + 0.9% Additional Medicare.
- Update frequency:
- Annual (wage base). Rates unchanged since 1990.
- Used by:
- Self-Employment Tax Calculator, FICA calculation in state pages
Nonpartisan tax policy research organization. Publishes comprehensive state income tax bracket data annually with downloadable Excel files. Widely cited in academic and policy research.
- Examples:
- State Individual Income Tax Rates and Brackets, 2025 — all 50 states + DC
- Update frequency:
- Annual (published January/February for current year)
- Used by:
- All 51 state income tax calculator pages
How We Keep Data Current
Different data types have different refresh cycles:
| Data Type | Refresh Method | Frequency |
|---|---|---|
| Mortgage rates | Live from FRED API via ISR | Hourly |
| I Bond rates | Live from Treasury API via ISR | Daily |
| CPI / Inflation data | Embedded BLS data | Updated when BLS publishes annual average |
| Federal tax brackets | Manual update, 3-source cross-validation | Annual (when IRS publishes Rev. Proc., Oct/Nov) |
| State tax brackets | Manual update from Tax Foundation Excel | Annual (when Tax Foundation publishes, Jan/Feb) |
| SS wage base / FICA | Manual update from SSA | Annual |
What Our Calculators Include and Exclude
We are transparent about the scope of each calculator. Tax calculators, for example, compute tax on ordinary income using standard deductions. They do not include:
- Tax credits (Child Tax Credit, EITC, education credits, etc.)
- Itemized deductions (mortgage interest, charitable giving, etc.)
- Capital gains (taxed at different rates)
- Other local income taxes (e.g. some OH/PA cities) — we include NYC when you select New York and opt in; data from Tax Foundation and official city/state sources
- Pre-tax deductions (401k, HSA, etc.) unless explicitly entered
Each calculator's methodology section lists exactly what it includes and excludes. We prefer to be precise about a smaller scope than to be approximate about a broader one.
Found an Error?
If you find a discrepancy between our calculator output and the official source data, we want to know. Please include:
- Which calculator and what inputs you used
- The result ClearFigure showed
- What you believe the correct result is
- The source you're comparing against (IRS publication number, URL, etc.)
We take accuracy reports seriously and will investigate and correct any verified errors promptly.