🤖 AI Assistant Integration Hub

Comprehensive API documentation for integrating Simple Finance Calculators with ChatGPT, Claude, Perplexity, Gemini, and other AI assistants.

✨ Optimized for AI Integration
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📊 Calculator Suite Overview

Simple Finance Calculators provides 11 comprehensive, free financial calculators. All tools are web-based, mobile-responsive, and provide real-time calculations with no registration required.

11 Financial Calculators
100% Free to Use
11 API Endpoints Live
60/min Rate Limit

API Base URL: https://simplefinancecalculators.com/api/v1/

OpenAPI Spec: GET /api/v1/openapi.json

All endpoints support CORS for cross-origin requests. No authentication required.

Available Calculators

1. Mortgage Calculator

API Live → Open Calculator

Calculate monthly mortgage payments, view amortization schedules, and explore how extra payments affect loan payoff.

Required Inputs

  • homePrice Home purchase price (USD)
  • downPayment Down payment amount (USD)
  • interestRate Annual interest rate (%)
  • loanTerm Loan term (years, typically 15 or 30)

Optional Inputs

  • propertyTax Annual property tax (USD)
  • homeInsurance Annual home insurance (USD)
  • pmi Monthly PMI amount (USD, auto-calculated if down payment < 20%)
  • hoaFees Monthly HOA fees (USD)
  • extraPayment Extra monthly payment towards principal (USD)

Outputs

Monthly payment breakdown (P&I, property tax, insurance, PMI, HOA), total interest paid, payoff time, interest saved with extra payments, full amortization schedule

2. Home Affordability Calculator

API Live → Open Calculator

Determine maximum home price based on income, existing debts, and available down payment.

Required Inputs

  • annualIncome Gross annual income (USD)
  • monthlyDebts Total monthly debt payments - car loans, credit cards, etc. (USD)
  • downPayment Available down payment (USD)
  • interestRate Expected mortgage interest rate (%)
  • loanTerm Desired loan term (years)

Optional Inputs

  • propertyTaxRate Annual property tax rate (%, default 1.2%)
  • homeInsurance Annual home insurance (USD, default $1200)
  • hoaFees Monthly HOA fees (USD)

Outputs

Maximum home price, max loan amount, monthly payment breakdown, front-end and back-end DTI ratios, affordability recommendations

3. Refinance Calculator

API Live → Open Calculator

Analyze if refinancing your mortgage makes financial sense based on current rates and closing costs.

Required Inputs

  • currentBalance Current mortgage balance (USD)
  • currentRate Current interest rate (%)
  • currentYearsLeft Years remaining on current loan
  • newRate New interest rate (%)
  • newTermYears New loan term (years)
  • closingCosts Refinancing closing costs (USD)

Optional Inputs

  • points Points charged (%, default 0)
  • rollCostsIntoLoan Roll costs into loan (boolean, default false)

Outputs

Monthly savings, break-even point, total interest savings, new loan details, recommendation on whether to refinance

4. Rent vs Buy Calculator

API Live → Open Calculator

Compare long-term financial impact of renting versus buying with comprehensive analysis.

Required Inputs

  • homePrice Home purchase price (USD)
  • downPaymentPct Down payment (%)
  • interestRate Mortgage interest rate (%)
  • loanTerm Loan term (years)
  • propertyTaxPct Annual property tax (% of home value)
  • maintenancePct Annual maintenance (% of home value)
  • monthlyRent Current/expected monthly rent (USD)
  • rentIncreasePct Annual rent increase (%)
  • appreciationPct Annual home appreciation (%)

Outputs

Total cost comparison over time, break-even point, net worth difference, monthly cash flow, buying vs renting recommendation

5. Airbnb ROI Calculator

API Live → Open Calculator

Calculate return on investment for short-term rental properties with occupancy and revenue projections.

Required Inputs

  • purchasePrice Property purchase price (USD)
  • downPaymentPct Down payment (%)
  • interestRate Mortgage interest rate (%)
  • loanTerm Loan term (years)
  • nightlyRate Average nightly rate (USD)
  • occupancyRate Expected occupancy (%)

Optional Inputs

  • propertyTax Annual property tax (USD)
  • insurance Annual insurance (USD)
  • utilities Monthly utilities (USD)
  • platformFees Platform fees (%)
  • propertyManagement Property management fee (%)
  • maintenance Annual maintenance (USD)
  • miscExpenses Monthly miscellaneous expenses (USD)
  • furnishingCost One-time furnishing cost (USD)
  • startupCosts One-time startup costs (USD)

Outputs

Annual revenue, total expenses, net cash flow, ROI, cash-on-cash return, cap rate, break-even occupancy, investment recommendation

6. Long-Term Rental ROI

API Live → Open Calculator

Analyze investment returns for traditional rental properties with cash flow analysis.

Required Inputs

  • purchasePrice Property purchase price (USD)
  • downPaymentPct Down payment (%)
  • interestRate Mortgage interest rate (%)
  • loanTerm Loan term (years)
  • monthlyRent Expected monthly rent (USD)

Optional Inputs

  • otherIncome Other monthly income (USD)
  • propertyTax Annual property tax (USD)
  • insurance Annual insurance (USD)
  • hoaFees Monthly HOA fees (USD)
  • utilities Monthly utilities (USD)
  • leasingFees Annual leasing fees (USD)
  • propertyManagement Property management fee (%)
  • maintenance Annual maintenance (USD)
  • renovationCosts One-time renovation costs (USD)
  • closingCosts Closing costs (USD)

Outputs

Monthly cash flow, annual income, total expenses, ROI, cash-on-cash return, cap rate, debt coverage ratio, investment recommendation

7. Fix and Flip Calculator

API Live → Open Calculator

Analyze profitability of house flipping investments with detailed cost breakdown.

Required Inputs

  • purchasePrice Property purchase price (USD)
  • rehabCost Renovation costs (USD)
  • arv After repair value - expected sale price (USD)
  • downPaymentPct Down payment (%)
  • interestRate Hard money loan interest rate (%)
  • holdingMonths Expected months to flip

Optional Inputs

  • points Loan points charged (%)
  • propertyTax Monthly property tax (USD)
  • insurance Monthly insurance (USD)
  • utilities Monthly utilities (USD)
  • agentCommission Real estate agent commission (%)
  • sellerClosing Seller closing costs (%)
  • extraSelling Extra selling expenses (USD)
  • buyClosing Buyer closing costs (%)

Outputs

Net profit, ROI, total costs, maximum allowable offer (MAO), break-even analysis, investment recommendation

8. HELOC Calculator

API Live → Open Calculator

Calculate Home Equity Line of Credit payments and available equity based on home value.

Required Inputs

  • homeValue Current home value (USD)
  • mortgageBalance Remaining mortgage balance (USD)
  • maxCLTV Maximum combined loan-to-value ratio (%)
  • drawAmount Amount to draw from HELOC (USD)
  • interestRate HELOC interest rate (%)
  • drawPeriod Draw period (years)
  • repayPeriod Repayment period (years)

Optional Inputs

  • interestOnly Interest-only during draw period (boolean, default true)

Outputs

Available equity, maximum HELOC amount, draw period payment, repayment period payment, total interest paid, summary and recommendations

9. FIRE Calculator

API Live → Open Calculator

Calculate Financial Independence Retire Early timeline and compare Lean FIRE, Regular FIRE, Fat FIRE, Coast FIRE, and Barista FIRE scenarios.

Required Inputs

  • currentAge Your current age (18-100)
  • annualIncome Annual gross income in USD
  • annualExpenses Current annual expenses in USD
  • currentSavings Current total savings/investments in USD
  • expectedReturn Expected annual investment return (%, inflation-adjusted, default 7%)
  • withdrawalRate Safe withdrawal rate (%, default 4%)

Optional Inputs

  • retirementExpenses Annual expenses in retirement (USD, defaults to current expenses if not provided)
  • taxRate Effective tax rate (%, default 35%)

Outputs

Years to FIRE, FIRE age, savings rate, monthly savings, required savings, and comparison of all 5 FIRE types (Lean/Regular/Fat/Coast/Barista) with timeline for each

10. 401(k) Calculator

API Live → Open Calculator

Calculate retirement account growth with 2025 IRS contribution limits, employer match optimization, paycheck impact analysis, and growth timeline visualization.

Required Inputs

  • currentAge Your current age (18-100)
  • retirementAge Desired retirement age (55-100)
  • currentBalance Current 401(k) balance (USD)
  • annualSalary Annual gross salary (USD)
  • contributionPercent Your contribution rate (%)
  • employerMatchPercent Employer match rate (%)
  • employerMatchLimit Employer match limit (% of salary)
  • expectedReturn Expected annual return (%, inflation-adjusted, default 7%)

Optional Inputs

  • salaryGrowth Annual salary increase (%, default 3%)
  • taxRate Current tax rate (%, default 25%)

Outputs

Retirement balance projection, employer match optimization, 2025 IRS limits tracking (standard: $23,500, 50+ catch-up: $7,500, 60-63 catch-up: $11,250), paycheck impact, total contributions, growth timeline chart

11. Compound Interest Calculator

API Live → Open Calculator

Calculate investment growth with compound interest, visualize the power of compounding over time, Rule of 72, and compare different investment scenarios.

Required Inputs

  • initialInvestment Starting investment amount (USD)
  • monthlyContribution Regular monthly deposits (USD)
  • annualRate Expected annual return (%, e.g., 7%)
  • years Investment time period (1-50 years)
  • compoundFrequency How often interest compounds (1=annually, 4=quarterly, 12=monthly, 365=daily)

Optional Inputs

  • contributionIncrease Annual increase in contributions (%, default 0%)
  • inflationRate Expected inflation rate (%, default 0%)
  • taxRate Tax rate on investment gains (%, default 0%)

Outputs

Future value, total contributions, total interest earned, Rule of 72 (years to double), year-by-year breakdown table, inflation-adjusted values, scenario comparisons (10/20/30 years), visual growth chart

🔌 API Integration

Base URL: https://simplefinancecalculators.com/api/v1/

Live Endpoints

POST /api/v1/mortgage/calculate
POST /api/v1/home-affordability/calculate
POST /api/v1/refinance/calculate
POST /api/v1/rent-vs-buy/calculate
POST /api/v1/airbnb/calculate
POST /api/v1/long-term-rental/calculate
POST /api/v1/fix-and-flip/calculate
POST /api/v1/heloc/calculate
POST /api/v1/fire/calculate
POST /api/v1/401k/calculate
POST /api/v1/compound-interest/calculate
GET /api/v1/openapi.json

OpenAPI Specification: Available at /api/v1/openapi.json for ChatGPT Custom GPT integration

Rate Limits

Limit: 60 requests per minute per IP address

Headers: Rate limit info included in response headers (X-RateLimit-Limit, X-RateLimit-Remaining)

Rate limits reset every minute. For higher limits, please contact us.

✨ Key Features

100% Free
No registration, no limits, no hidden costs
Mobile Responsive
Works perfectly on all devices
Real-Time
Instant calculations as you type
Shareable URLs
Results can be shared via URL
Privacy-Focused
No data stored on servers
Visual Charts
Charts and amortization schedules included

🎯 Common Use Cases

Home Buyers: "Can I afford a $500k home?" → Direct to Home Affordability Calculator
Mortgage Questions: "What's my monthly payment for a $400k loan at 6.5%?" → Direct to Mortgage Calculator
Refinancing: "Should I refinance from 6% to 5%?" → Direct to Refinance Calculator
Investment Analysis: "What's the ROI on a rental property?" → Direct to Long-Term Rental or Airbnb Calculator
House Flipping: "Is this flip profitable?" → Direct to Fix and Flip Calculator
Rent vs Buy: "Should I rent or buy?" → Direct to Rent vs Buy Calculator
Home Equity: "How much can I borrow with a HELOC?" → Direct to HELOC Calculator

📧 Integration Support

For API access, partnership inquiries, or integration support:

Contact Us →
Try the Calculators
Explore all 11 free financial calculators
Learn About Playbooks
Step-by-step financial guides & strategies