Methodology
How CalcFi works.
Every CalcFi calculator is built on verified government and industry data, reviewed regularly, and designed to give you honest, accurate results. Not estimates that pad someone else's bottom line.
Written by Jere Salmisto · Reviewed by CalcFi Editorial · Last verified:
Jere Salmisto
Founder + sole maintainer
Built CalcFi to make money math transparent. Estonian + Finnish founder, US-focused public-data calculator stack.
Guiding principles
- 01
Primary sources only
We pull tax rates, income data, and financial benchmarks directly from government agencies and authoritative industry bodies, not from other calculator sites or aggregators that may be out of date.
- 02
No sponsored results
CalcFi has no financial products to sell. Our calculations are not influenced by affiliate relationships, and we never adjust results to push users toward higher-cost options.
- 03
Methodology transparency
Every formula we use is documented here. If you're a CPA, financial advisor, or just a curious user, you can verify our math and call us out if something's wrong.
- 04
Conservative defaults
Where assumptions are required (investment returns, inflation, insurance costs), we use historically conservative defaults and clearly label all assumptions so you can adjust them.
Data sources
CalcFi pulls data from the following primary sources. We do not use crowd-sourced data or unverified third-party APIs for any core calculations.
IRS (Internal Revenue Service)
Tax brackets, standard deductions, contribution limits, capital gains rates, estate tax thresholds, and all federal tax figures.
Bureau of Labor Statistics (BLS)
Salary data by occupation and state, inflation (CPI) indices, employment cost indexes, and wage percentile data.
U.S. Census Bureau
Household income data, median income by state, cost-of-living estimates, and demographic breakdowns for financial context.
Federal Reserve
Interest rate benchmarks (Fed Funds Rate, prime rate), Survey of Consumer Finances (net worth and retirement savings by age), and credit data.
Zillow Research
Median home prices by state and city, home appreciation rates, and rental price data for rent-vs-buy and mortgage calculators.
National Association of Realtors (NAR)
Median home sales prices, down payment trends, buyer demographics, and housing market indicators.
Tax Foundation
State income tax rates, sales tax data, effective tax rate analysis, and state tax competitiveness rankings.
Social Security Administration (SSA)
Benefit calculation formulas, full retirement age tables, bend points, COLA adjustments, and earnings test thresholds.
Department of Defense / DFAS
Basic Allowance for Housing (BAH) rates, military pay tables, Blended Retirement System formulas, and TSP matching rules.
Update schedule
Financial data changes constantly. Here's how often we update each category and what triggers a review.
| Data Category | Frequency | Update Trigger |
|---|---|---|
| Tax brackets & rates | Annually | When IRS releases inflation adjustments (typically October/November) |
| Contribution limits (401k, IRA, HSA) | Annually | When IRS announces limits for the new tax year |
| Standard deductions | Annually | IRS Revenue Procedures released each fall |
| Home prices & housing data | Quarterly | Zillow and NAR quarterly reports |
| Salary data | Annually | BLS Occupational Employment Statistics release |
| Interest rates | Monthly | Federal Reserve rate decisions and market benchmarks |
| Social Security bend points & COLA | Annually | SSA October announcements |
| State tax rates | Annually | State legislative sessions (January–June) |
| BAH rates (military) | Annually | DoD rate surveys released in December |
Calculator-specific methodology
Here's a breakdown of the formulas and logic behind our most-used calculators.
Mortgage Payment
Standard amortization: M = P[r(1+r)^n]/[(1+r)^n-1]Where P = principal, r = monthly interest rate, n = number of payments. We add PMI (0.5–1.5% annually) when down payment is under 20%, property tax (sourced from state averages), and homeowners insurance estimates. Total PITI payment shown.
Tax Bracket Calculator
Progressive marginal taxation with inflation-adjusted bracketsWe apply each bracket progressively. Only income in a given bracket is taxed at that rate. We include the standard deduction, then calculate federal tax, Social Security tax (6.2% up to wage base), Medicare tax (1.45% + 0.9% above $200K), and optionally state income tax using Tax Foundation data.
Retirement Savings
FV = PV(1+r)^n + PMT × [(1+r)^n - 1]/rFuture value calculation using compound growth on existing savings plus recurring contributions. Inflation-adjusted projections use real rate of return (nominal return minus assumed 2.5–3% inflation). Monte Carlo scenarios shown for conservative, moderate, and aggressive portfolios.
FIRE Number
FIRE Number = Annual Expenses / Safe Withdrawal RateBased on the Trinity Study's 4% rule (25x annual expenses). We also show 3% (33x, ultra-conservative) and 3.5% (28.6x) variants. The years-to-FIRE calculation uses compound growth of current savings plus annual contributions.
Self-Employment Tax
SE Tax = Net Self-Employment Income × 0.9235 × 0.153The 92.35% multiplier accounts for the deductible half of SE tax. The 15.3% covers 12.4% Social Security (up to wage base) + 2.9% Medicare. Half of SE tax is then deductible from federal income tax. QBI deduction (up to 20%) applied where applicable.
Debt Payoff
Amortization schedule with snowball/avalanche optimizationWe model each debt's minimum payment schedule, then apply extra payments using either the avalanche method (highest APR first, mathematically optimal) or snowball method (smallest balance first, behaviorally effective). Total interest saved and payoff date difference shown for both approaches.
Compound Interest
A = P(1 + r/n)^(nt) + PMT × [(1 + r/n)^(nt) - 1]/(r/n)Where P = principal, r = annual rate, n = compounding frequency, t = years, PMT = regular contribution. We support daily, monthly, quarterly, and annual compounding. Inflation-adjusted final value shown using historical CPI averages.
Money Analysis model
The Money Analysis reads the calculator results you have saved as one picture across three dimensions: housing pressure, debt pressure, and cash buffer. It is a calculation summary of inputs you provided: not a credit score, not a personalized recommendation, and not financial advice. Each dimension is computed only when you have saved enough calculators to populate it.
Housing pressure
Formula: housing_cost / take_home_pay × 100
Benchmark: The 30% threshold mirrors the U.S. Department of Housing and Urban Development (HUD) definition of cost burden: households spending more than 30% of gross income on housing are classified as cost-burdened. Housing pressure above 50% of take-home triggers a maximum-pressure score of 0/100 in this model.
Source: HUD Affordable Housing — Definition of Cost Burden ↗
Debt pressure
Formula: total_debt_payments / take_home_pay × 100
Benchmark: The 36% threshold mirrors the back-end debt-to-income (DTI) ceiling in the Fannie Mae Selling Guide for conventional conforming loans. Debt above 40% of take-home triggers a maximum-pressure score of 0/100 in this model.
Source: Fannie Mae Selling Guide ↗
Cash buffer
Formula: emergency_fund / monthly_expenses = months of coverage.
Benchmark: 3 to 6 months of expenses, per CFPB consumer guidance on emergency savings. Cash buffer caps at 100/100 once 6+ months of coverage is reached.
Source: CFPB — Start Small, Save Up ↗
Use our data
Public anonymous aggregates for journalists, researchers, and developers. CC BY 4.0 licensed. K-anonymity enforced (count >= 10): no PII, no raw values, no individual users. No auth required.
Quick start
curl -s "https://calcfi.app/api/insights/calc-aggregates?slug=mortgage-payment&state=TX&since=2026-04-01" | jq .Sample response
{
"topic": "calc-aggregates",
"since": "2026-04-01",
"count": 3,
"next_cursor": null,
"rows": [
{ "day": "2026-04-15", "calc_slug": "mortgage-payment", "city": "austin", "state": "TX", "result_band": "2-2.5k", "count_runs": 18 },
{ "day": "2026-04-15", "calc_slug": "mortgage-payment", "city": "dallas", "state": "TX", "result_band": "1.5-2k", "count_runs": 22 },
{ "day": "2026-04-16", "calc_slug": "mortgage-payment", "city": "houston", "state": "TX", "result_band": "1.5-2k", "count_runs": 14 }
]
}License: CC BY 4.0. Attribution to calcfi.app requested. Building something with this data? Email editorial@calcfi.app. We love seeing it.
Cross-analysis methodology
Money Analysis doesn't just store your numbers. It flags where they conflict with each other against primary-source thresholds. Each flag is a specific rule that fires when your inputs cross an evidence-based boundary. The math behind each boundary is documented below so you can verify the threshold yourself. Four flags are currently in production.
Retirement Contribution vs. High-APR Debt
Rule: Fires when you are contributing to a retirement account while carrying revolving debt with APR above 10%.
Why:The average commercial-bank credit-card interest rate is 22.30% (Federal Reserve G.19, May 2026). The S&P 500's long-run nominal return is ~10% (Macrotrends 1927–2026, 100-year average). Every $1 of carried high-APR debt costs more annually than the same $1 earns in an index fund. Pay the guaranteed-loss instrument before chasing the probabilistic gain.
Sources: Federal Reserve G.19 — series TERMCBCCALLNS ↗ · Macrotrends S&P 500 historical annual returns ↗
House-Poor Threshold
Rule:Fires when mortgage P&I exceeds 35% of gross monthly income AND the emergency fund covers less than 3 months of essential expenses.
Why:The CFPB Qualified Mortgage rule caps total DTI at 43%, but P&I alone over 35% leaves little room for property tax, insurance, and maintenance escalation (NAIC data shows homeowner insurance up ~30% nationally since 2020). Add a thin emergency buffer and one income shock forces a distressed sale.
Sources: CFPB Regulation Z §1026.43 — Qualified Mortgage ↗ · NAIC Homeowners Insurance Market Report ↗
Missing HSA Triple-Tax-Advantage
Rule: Fires when you are on a high-deductible health plan, your HSA contribution is $0, and you are contributing to a 401(k).
Why: HSAs are the only US tax-advantaged account that is pre-tax in, tax-free growth, and tax-free out on qualified medical expenses. After age 65, the account functions like a traditional IRA for non-medical withdrawals. 2026 limits per IRS Rev. Proc. 2025-19: $4,400 self-only / $8,750 family. Skipping the HSA while funding a 401(k) leaves the most efficient tax shelter unused.
Sources: IRS Rev. Proc. 2025-19 — 2026 HSA limits ↗ · IRC §223 — HSA statutory authority ↗
Lifestyle Inflation
Rule: Fires when annual income exceeds $100,000 AND monthly savings rate is under 10%.
Why: The BEA Personal Saving Rate sits at ~5% nationally. High earners with savings rates below 10% typically allocate raises to fixed costs (bigger home, car upgrade, lifestyle creep) rather than capping discretionary spend at the prior salary level. The compounding gap: 5 years of 5% savings vs. 20% savings on $150k income is roughly $45k vs. $180k in invested assets.
These rules are heuristics, not personalized advice. CalcFi flags patterns and points to the primary source so you can verify the threshold yourself. The methodology is open and reviewable. Source on GitHub ↗.
Important limitations
CalcFi provides educational estimates, not professional financial advice. Our calculators are designed to give you accurate ballpark figures to inform your decisions, but every financial situation is unique.
Tax calculations are based on federal rules plus state averages. Your actual tax liability depends on deductions, credits, alternative minimum tax, and other factors specific to your situation. Always consult a CPA or tax professional for filing decisions.
Investment projections use historical return assumptions (e.g., 7% real return for diversified equity portfolios) but past performance does not guarantee future results. Markets can and do underperform historical averages for extended periods.
Mortgage and loan estimates do not account for lender-specific fees, points, or underwriting criteria. Actual rates and costs vary by lender, credit score, and market conditions. Get quotes from at least three lenders before committing.
Found an error?
We take accuracy seriously. If you spot a calculation that looks wrong or a data source that's out of date, please let us know.
Report an issueAll CalcFi open-data pipelines are permanently archived at the Software Heritage Archive (8 repositories, indexed 2026-05-26 UTC). Each repository has a citable SWHID identifier. See the Developers page for the full archive list and permanent identifiers.