# SmartFin

> Free financial calculators, S&P 500 stock comparison tools, and backtesting utilities at smartfin.fyi. Every figure comes from SmartFin's own calculation engine. Educational tools only, not financial advice.

Every calculator page provides full mathematical methodology, inputs, formulas, rounding, exclusions, and a reproducible canonical URL payload.

## Data Methodology

- **Calculators:** Calculated from visitor inputs and explicit assumptions; nothing is projected beyond stated inputs.
- **Historical Returns:** Driven by daily closing prices adjusted for stock splits, with dividends reinvested, for current S&P 500 companies and major index funds.
- **Exclusions:** Excludes taxes, trading fees, expense ratios beyond share price, and currency conversion.

## Primary Engines & Tools

- [Compare Two Stocks](https://smartfin.fyi/compare-two-stocks.html): Compares two S&P 500 stocks/ETFs over identical dates for total return, CAGR, max drawdown, and recovery duration.
- [Investment Simulator](https://smartfin.fyi/simulator.html): Backtests single-asset strategies across lump-sum, monthly DCA, and buy-the-dip approaches.
- [FIRE Calculator](https://smartfin.fyi/fire-calculator.html): Calculates Coast FIRE, FI numbers, and target years based on a chosen withdrawal rate and inflation.
- [Historical Returns Index](https://smartfin.fyi/historical-returns.html): Index of stock tools and historical ticker pages such as [Apple (AAPL)](https://smartfin.fyi/stocks/aapl) and [S&P 500 (SPY)](https://smartfin.fyi/stocks/spy).

## Investing & Savings Calculators

- [Investment Growth Calculator](https://smartfin.fyi/investment-calculator.html): Projects growth from an initial principal plus recurring contributions.
- [Compound Interest Calculator](https://smartfin.fyi/compound-interest-calculator.html): Evaluates compound growth across varied compounding frequencies.
- [CAGR Calculator](https://smartfin.fyi/cagr-calculator.html): Computes compound annual growth rate between initial and final values.
- [Rule of 72](https://smartfin.fyi/rule-of-72.html): Estimates doubling time at a fixed rate versus exact mathematical log equations.
- [Inflation Calculator](https://smartfin.fyi/inflation-calculator.html): Calculates purchasing power degradation over time.
- [Future Value Calculator](https://smartfin.fyi/future-value-calculator.html): Solves for the future worth of present capital.
- [Present Value Calculator](https://smartfin.fyi/present-value-calculator.html): Discounts future lump sums back to today's purchasing power.
- [Simple Interest Calculator](https://smartfin.fyi/simple-interest-calculator.html): Models non-compounding interest accrual.

## Loan Calculators

- [Mortgage Calculator](https://smartfin.fyi/mortgage-calculator.html): Calculates monthly principal/interest payments and total interest cost.
- [Mortgage Payoff Calculator](https://smartfin.fyi/mortgage-payoff-calculator.html): Evaluates extra monthly or lump-sum principal payments to accelerate term reduction.
- [Down Payment Calculator](https://smartfin.fyi/down-payment-calculator.html): Estimates required down payment amounts and savings timelines.
- [Car Loan Calculator](https://smartfin.fyi/car-loan-calculator.html): Computes auto loan payment schedules and overall borrowing costs.
- [Student Loan Calculator](https://smartfin.fyi/student-loan-calculator.html): Models debt payoff speed and total interest under extra payment scenarios.
- [Refinance Calculator](https://smartfin.fyi/refinance-calculator.html): Analyzes new loan terms, net savings, and break-even payoff dates.

## Retirement Calculators

- [Withdrawal Calculator](https://smartfin.fyi/withdrawal-calculator.html): Models how long savings last, or how much can be withdrawn, at chosen withdrawal rates.

## Business & Decision Calculators

- [Rent vs Buy Calculator](https://smartfin.fyi/rent-vs-buy-calculator.html): Year-by-year net worth trajectory comparison between renting and purchasing real estate.
- [Savings vs Investing Calculator](https://smartfin.fyi/savings-vs-investing-calculator.html): Compares a savings account against investing the same money.
- [ROI Calculator](https://smartfin.fyi/roi-calculator.html): Calculates return on investment from the amount put in and its final value.
- [Profit Margin Calculator](https://smartfin.fyi/profit-margin-calculator.html): Calculates profit margin from revenue and total costs.

## AI Agents & Developer Infrastructure

- [Model Context Protocol (MCP) Endpoint](https://smartfin.fyi/mcp): Live Streamable-HTTP / SSE endpoint providing direct AI agent access to calculation tools (`fyi.smartfin/smartfin`).
- [mcp.market Server Listing](https://mcp.market/server/smartfin): Verified registry listing on mcp.market.
- [Embeddable Widgets](https://smartfin.fyi/embed.html): Zero-dependency HTML iframe widgets for financial blogs and publisher embeds.

## Optional

- [About SmartFin](https://smartfin.fyi/about.html): Overview of SmartFin's architecture, independent publishing stance, and methodology.
- [Terms of Service](https://smartfin.fyi/terms.html): Usage terms, non-advice disclaimers, and educational guidelines.
- [Privacy Policy](https://smartfin.fyi/privacy-policy.html): Privacy practices and third-party vendor disclosures.