Methodology & Assumptions
Full disclosure of all data sources, tax logic, calculation methodologies, and update frequencies powering QuantCurb's financial modeling.
Last Updated: September 18, 2026
Core Principles
Mathematical rigor and algorithmic sovereignty
Precision Over Estimation
All calculations use exact mathematical formulas, not approximations. We employ reducing balance amortization, compound interest with continuous compounding where applicable, and precise tax bracket marginal calculations.
Transparent Data Sources
Every data point is traceable to official government sources, central bank publications, or verified financial institutions. We cite IRS tax tables, Federal Reserve economic data, and State Department of Revenue publications.
Regular Updates
Tax brackets, contribution limits, and regulatory thresholds are updated annually (typically January-February). Interest rate data and currency exchange rates refresh monthly. Market sentiment analysis updates in real-time via AI.
Tax & Salary Calculations
2026 tax year specifications
Federal Tax Brackets (2026)
10%: $0 - $12,400
12%: $12,401 - $50,400
22%: $50,401 - $105,700
24%: $105,701 - $201,775
32%: $201,776 - $256,225
35%: $256,226 - $640,600
37%: $640,601+
Source: IRS Revenue Procedure 2025-32 (Single Filer)
FICA & Payroll Taxes
Social Security: 6.2%
Wage base limit: $184,500 (2026)
Medicare: 1.45%
Additional 0.9% on income > $200k
Self-Employment: 15.3%
(12.4% SS + 2.9% Medicare)
State Tax Handling
Our Salary Estimator models all 50 states' income tax structures. For states with progressive brackets (e.g., California, New York), we use marginal bracket math. For flat-tax states (e.g., Illinois, Colorado), we apply the single rate. Nine states have no income tax (Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington, Wyoming, New Hampshire).
Loan & Mortgage Calculations
Amortization methodology and assumptions
EMI Formula (Reducing Balance)
EMI = P ร r ร (1 + r)^n / ((1 + r)^n - 1)Where:
P = Principal loan amount
r = Monthly interest rate (annual rate / 12)
n = Total number of monthly payments
Mortgage PITI Breakdown
Principal & Interest
Standard amortization formula (above)
Property Taxes
User input, typically 0.5-2.5% of home value annually
Insurance
User input, avg $800-2000/year
PMI (if LTV > 80%)
0.3-1.5% of loan amount annually
โ ๏ธ Prepayment Assumptions
When modeling extra principal payments, we assume: (1) Payments are applied immediately to principal, (2) No prepayment penalties, (3) Monthly payment remains constant unless explicitly recalculated. Always verify your loan agreement allows penalty-free prepayment.
Investment & Retirement Calculations
Growth projections and compounding logic
Compound Interest (Future Value)
FV = PV ร (1 + r)^t + PMT ร [((1 + r)^t - 1) / r]Where:
PV = Present value (initial investment)
PMT = Periodic contribution (monthly SIP)
r = Periodic return rate
t = Number of periods
2026 Retirement Contribution Limits
$24,500
401(k) Limit
+$8,000 catch-up (50+)
$7,500
IRA Limit
+$1,100 catch-up (50+)
$7,500
Roth IRA Limit
Income phase-outs apply
Source: IRS Notice 2025-67
FIRE Planning (4% Rule)
The "4% Safe Withdrawal Rate" is based on the Trinity Study (1998, updated 2020). It models a 95% success probability of sustaining withdrawals over 30 years with a 50/50 stock/bond portfolio.
Freedom Number = Annual Expenses ร 25
Example: $60,000/year ร 25 = $1,500,000 portfolio target
Currency & Market Data
Exchange rates and AI sentiment analysis
Forex Exchange Rates
Currency conversion rates are based on interbank mid-market rates (the midpoint between buy and sell prices). These represent the "true" market rate without retail markup. Data refreshes monthly from central bank publications and OECD Economic Outlook reports.
Note: Actual consumer rates at banks/exchanges typically include 1-5% markup. Our tool shows the benchmark for auditing provider spreads.
AI Market Sentiment
Market insights and sentiment analysis are generated using Google's Gemini AI (gemini-3-flash-preview for data synthesis, gemini-3-pro-preview for advice). The AI analyzes: (1) Interest rate differentials, (2) Geopolitical stability indices, (3) Historical volatility patterns, (4) Institutional vs retail app ecosystem trends.
Important Limitations
What our calculators DO NOT account for
Individual Circumstances
Our tools use standardized assumptions. They cannot account for: specific state tax credits, municipal tax variations, unique loan terms, employer-specific benefit structures, or personal risk tolerance.
Market Volatility
Investment projections assume constant returns. Real markets experience volatility, sequence-of-returns risk, and black swan events. Historical performance does not guarantee future results.
Regulatory Changes
Tax laws, contribution limits, and financial regulations change. Congress can modify tax brackets, deduction limits, and retirement account rules. Always verify current year regulations with official IRS publications or a licensed tax professional.