Sources & References
Reckonly uses only primary and official sources for all rate data, formulas, and classification standards. Secondary sources — blogs, news articles, competitor calculators — are never used as a basis for any calculation. Below is the complete source list by calculator.
- 2025 Federal Tax Brackets: IRS Revenue Procedure 2024-61 — official inflation-adjusted bracket thresholds
- Standard Deduction Amounts: IRS Publication 501 (2025) — $15,000 single, $30,000 married filing jointly
- Filing Status Definitions: IRS Publication 501
- Progressive Tax System Formula: IRS Form 1040 Instructions (2024)
Note: Does not include state taxes, FICA, AMT, or tax credits. For complete tax liability, consult a qualified tax professional.
- Amortization Formula: M = P[r(1+r)^n]/[(1+r)^n-1] — standard fixed-rate mortgage formula per CFPB guidelines
- PMI Reference: Consumer Financial Protection Bureau (CFPB) — "When can I remove private mortgage insurance (PMI) from my loan?"
- APR Calculation Method: Truth in Lending Act (TILA), Regulation Z
- EMI Formula: Standard fixed-rate loan amortization — same mathematical basis as CFPB mortgage formula
- APR Definition: Consumer Financial Protection Bureau — "What is the difference between a mortgage interest rate and an APR?"
- Compound Interest Formula: A = P(1 + r/n)^(nt) — standard financial mathematics formula
- Rule of 72: Standard financial approximation — verified against exact compound interest calculation
- S&P 500 Historical Return Reference: 7% real (inflation-adjusted) — widely cited in financial planning literature based on long-term index data
- Future Value Formula: FV = PV(1+r)^n + PMT[(1+r)^n-1]/r — standard time value of money formula
- 4% Withdrawal Rule: Based on the "Trinity Study" (Cooley, Hubbard & Walz, 1998) — widely referenced in retirement planning
- Inflation Adjustment: Real rate of return = (1 + nominal rate) / (1 + inflation rate) - 1
- Exchange Rates: European Central Bank (ECB) — Daily Reference Rates API (api.frankfurter.app), updated every business day
- Rate Type: Mid-market reference rates — not buy/sell rates from any commercial institution
Actual transaction rates at banks and currency exchanges will differ due to spreads and fees.
- BMI Formula: BMI = weight(kg) / height(m)² — World Health Organization standard
- BMI Categories: WHO — "Body Mass Index (BMI)" classification: Underweight <18.5, Normal 18.5–24.9, Overweight 25–29.9, Obese ≥30
- Imperial Formula: BMI = 703 × weight(lb) / height(in)² — CDC standard conversion
BMI is a screening tool only. It does not account for muscle mass, bone density, or body composition. Consult a healthcare professional for medical advice.
- Required Monthly Payment Formula: PMT = FV × r / [(1+r)^n - 1] — standard annuity formula
- Time to Goal Formula: n = log(FV×r/PMT + 1) / log(1+r)
- Fuel Cost Formula: Cost = (Distance ÷ Fuel Efficiency) × Fuel Price
- MPG to L/100km Conversion: L/100km = 235.21 ÷ MPG — US DOE standard conversion factor
- Fuel efficiency reference standard: US Environmental Protection Agency (EPA) fuel economy measurement methodology
- Percentage Formula: Standard arithmetic — P = (Part ÷ Whole) × 100
- Age Calculation: Gregorian calendar date arithmetic — accounts for leap years
- Date Difference: ISO 8601 date arithmetic
- Unit Conversion Factors: NIST (National Institute of Standards and Technology) — Special Publication 811, Guide for the Use of the International System of Units (SI)
- Temperature Conversions: NIST standard formulas — °F = (°C × 9/5) + 32; K = °C + 273.15
Never used as a source: SEO blogs, news articles, competitor calculator websites, AI-generated content, or any unverified secondary source — regardless of how authoritative they appear in search results.
See also: Methodology · About · Changelog
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