# Stupidly Clever

> Free online calculators, tools, and data explorers for finance, health, global comparisons, physics, statistics, and developer utilities. Also available as a REST API and MCP server for AI agents and developers.

## API & MCP Access

- Base URL: [https://api.stupidlyclever.com/v1/](https://api.stupidlyclever.com/v1/)
- MCP endpoint: [https://api.stupidlyclever.com/mcp](https://api.stupidlyclever.com/mcp)
- OpenAPI spec: [https://api.stupidlyclever.com/openapi.json](https://api.stupidlyclever.com/openapi.json)
- Documentation: [https://api.stupidlyclever.com/docs](https://api.stupidlyclever.com/docs)
- Authentication: Bearer API key, required for both the REST API and MCP endpoint. Get a key at [https://www.stupidlyclever.com/dashboard](https://www.stupidlyclever.com/dashboard)
- Pricing: [https://www.stupidlyclever.com/pricing](https://www.stupidlyclever.com/pricing)

The MCP server at [https://api.stupidlyclever.com/mcp](https://api.stupidlyclever.com/mcp) exposes the same tools as the REST API in MCP tool format. Compatible with Claude, OpenAI Responses API, and any MCP-compatible client.

## Date & Time Tools

- [Business Days Calculator](https://www.stupidlyclever.com/business-days): Count or add business days, excluding weekends and public holidays by country
- [Public Holidays](https://www.stupidlyclever.com/public-holidays): Look up public holidays for any country and year
- [Date Difference](https://www.stupidlyclever.com/date-diff): Calculate the duration between two dates in days, weeks, months, or years
- [Time Duration](https://www.stupidlyclever.com/time-duration): Compute elapsed time between two date-times with precision
- [Date Format Converter](https://www.stupidlyclever.com/date-format-converter): Convert dates between ISO 8601, RFC 2822, Unix timestamp, and other formats
- [Timezone Conversion](https://www.stupidlyclever.com/timezone-conversion): Convert times between any two timezones worldwide
- [Unix Timestamp](https://www.stupidlyclever.com/unix-timestamp): Convert between Unix timestamps and human-readable dates
- [Fiscal Year](https://www.stupidlyclever.com/fiscal-year): Determine the fiscal year for any date across different country standards
- [Week Number](https://www.stupidlyclever.com/week-number): Find the ISO week number for any date
- [Countdown](https://www.stupidlyclever.com/countdown): Count down to a future date excluding weekends or holidays

## Finance Calculators

- [Compound Interest](https://www.stupidlyclever.com/compound-interest): Calculate compound interest with flexible compounding frequencies
- [Mortgage Calculator](https://www.stupidlyclever.com/mortgage): Compute monthly payments, total interest, and amortisation schedules
- [Loan Comparison](https://www.stupidlyclever.com/loan-comparison): Compare two loan offers side by side on total cost
- [VAT Calculator](https://www.stupidlyclever.com/vat): Add or remove VAT for any country's rate
- [Invoice Generator](https://www.stupidlyclever.com/invoice): Create and calculate invoices with line items, tax, and discounts
- [Late Payment Interest](https://www.stupidlyclever.com/late-payment-interest): Calculate statutory late payment interest on overdue invoices
- [Invoice Interest](https://www.stupidlyclever.com/invoice-interest): Compute interest charges on unpaid invoices
- [Benchmark Rates](https://www.stupidlyclever.com/benchmark-rates): Look up central bank and benchmark interest rates by country
- [Currency Converter](https://www.stupidlyclever.com/currency-converter): Convert between world currencies using live rates
- [NPV Calculator](https://www.stupidlyclever.com/npv): Net present value of a series of cash flows at a given discount rate
- [Bond Price Calculator](https://www.stupidlyclever.com/bond-price): Price a bond given coupon rate, yield to maturity, and time to maturity
- [Share Price (DDM)](https://www.stupidlyclever.com/share-price): Intrinsic value of a stock using the dividend discount model
- [Income Tax Calculator](https://www.stupidlyclever.com/income-tax): Estimate income tax and take-home pay across multiple countries
- [Take-Home Pay](https://www.stupidlyclever.com/take-home-pay): Net pay after tax and deductions by country
- [Inflation-Adjusted Return](https://www.stupidlyclever.com/inflation-adjusted-return): Calculate real returns after accounting for inflation
- [Purchasing Power](https://www.stupidlyclever.com/purchasing-power): How inflation erodes the purchasing power of money over time
- [Break-Even Calculator](https://www.stupidlyclever.com/break-even): Find break-even point in units and revenue
- [Retirement Savings](https://www.stupidlyclever.com/retirement-savings): Project retirement savings growth with contributions and withdrawals
- [Safe Withdrawal Rate](https://www.stupidlyclever.com/safe-withdrawal-rate): Determine a sustainable withdrawal rate from a retirement portfolio
- [Monte Carlo Retirement](https://www.stupidlyclever.com/monte-carlo-retirement): Simulate thousands of retirement outcomes with Monte Carlo analysis
- [Tax-Loss Harvesting](https://www.stupidlyclever.com/tax-loss-harvesting): Model the tax savings from harvesting investment losses
- [Social Security Break-Even](https://www.stupidlyclever.com/social-security-break-even): Find the age at which delaying Social Security benefits pays off
- [Portfolio Rebalancing](https://www.stupidlyclever.com/portfolio-rebalancing): Calculate trades needed to rebalance a portfolio to target allocations
- [Kelly Criterion](https://www.stupidlyclever.com/kelly-criterion): Optimal position sizing for investments and bets using Kelly's formula
- [Black-Scholes](https://www.stupidlyclever.com/black-scholes): Price European call and put options using the Black-Scholes model
- [ROAS Calculator](https://www.stupidlyclever.com/roas-calculator): Return on ad spend calculator for marketing campaigns
- [Email Marketing ROI](https://www.stupidlyclever.com/email-marketing-roi): Calculate return on investment for email marketing campaigns
- [Influencer ROI](https://www.stupidlyclever.com/influencer-roi): Estimate ROI for influencer marketing spend

## Property & Housing

- [House Price to Income](https://www.stupidlyclever.com/house-price-to-income): Compare property prices relative to local income levels
- [Max Affordable Property](https://www.stupidlyclever.com/max-affordable-property): Maximum property value based on income and deposit
- [Mortgage Stress Test](https://www.stupidlyclever.com/mortgage-stress-test): Test affordability under higher interest rate scenarios (UK, Canada)
- [Rental Yield](https://www.stupidlyclever.com/rental-yield): Calculate gross and net rental yield on investment property
- [Buy vs Rent](https://www.stupidlyclever.com/buy-vs-rent-full): Full financial comparison of buying vs renting a home
- [Home Renovation Cost](https://www.stupidlyclever.com/home-renovation): Estimate renovation costs by room type and finish level

## Investing & Corporate Finance

- [WACC Calculator](https://www.stupidlyclever.com/wacc): Weighted average cost of capital with debt and equity components
- [CAPM Calculator](https://www.stupidlyclever.com/capm): Expected return using the Capital Asset Pricing Model
- [Levered / Unlevered Beta](https://www.stupidlyclever.com/levered-beta): Adjust beta for financial leverage using the Hamada equation
- [Sector Beta](https://www.stupidlyclever.com/sector-beta): Industry-level beta values from Damodaran data
- [Risk-Free Rate](https://www.stupidlyclever.com/risk-free-rate): Current risk-free rates by country and currency
- [Market Risk Premium](https://www.stupidlyclever.com/market-risk-premium): Equity risk premium by country from Damodaran
- [Sharpe Ratio](https://www.stupidlyclever.com/sharpe-ratio): Risk-adjusted return using Sharpe and Sortino ratios
- [S&P 500 Returns](https://www.stupidlyclever.com/sp500-returns): Historical S&P 500 annual and cumulative returns calculator
- [Historical Index Volatility](https://www.stupidlyclever.com/historical-index-volatility): Volatility of major market indices over selected periods
- [Yield Curve](https://www.stupidlyclever.com/yield-curve): US Treasury yield curve — current and historical
- [Altman Z-Score](https://www.stupidlyclever.com/altman-z-score): Predict corporate bankruptcy risk using the Altman Z-Score model
- [Piotroski F-Score](https://www.stupidlyclever.com/piotroski-f-score): Assess financial strength using Piotroski's 9-point scoring system
- [DuPont Analysis](https://www.stupidlyclever.com/dupont-analysis): Decompose return on equity into its component drivers
- [Free Cash Flow](https://www.stupidlyclever.com/free-cash-flow): Calculate free cash flow and FCF margin from financial statements
- [Valuation Multiples](https://www.stupidlyclever.com/valuation-multiples): P/E, EV/EBITDA, and other valuation ratio benchmarks by sector
- [Liquidity Ratios](https://www.stupidlyclever.com/liquidity-ratios): Current ratio, quick ratio, and cash ratio calculator
- [Solvency Ratios](https://www.stupidlyclever.com/solvency-ratios): Debt-to-equity, interest coverage, and other solvency metrics
- [Profitability Ratios](https://www.stupidlyclever.com/profitability-ratios): Gross margin, net margin, ROA, and ROE calculator
- [Efficiency Ratios](https://www.stupidlyclever.com/efficiency-ratios): Asset turnover, inventory turnover, and receivables days
- [Startup Valuation](https://www.stupidlyclever.com/startup-valuation): Pre-money valuation using multiple methods (Berkus, Scorecard, etc.)

## Business Tools

- [Startup Survival Rates](https://www.stupidlyclever.com/startup-survival): BLS data on business survival rates by age and industry
- [BLS Business Employment Dynamics](https://www.stupidlyclever.com/bls-bed-explorer): Interactive explorer for BLS establishment birth, survival, and death data
- [Market Sizing](https://www.stupidlyclever.com/market-sizing): TAM / SAM / SOM market size estimator
- [SaaS Revenue Model](https://www.stupidlyclever.com/saas-revenue): Project SaaS MRR, ARR, churn, and LTV
- [Customer LTV](https://www.stupidlyclever.com/customer-ltv): Lifetime value of a customer given retention and margin
- [Freelance Rate](https://www.stupidlyclever.com/freelance-rate): Calculate a day rate or hourly rate from a target annual income
- [Employer Cost](https://www.stupidlyclever.com/employer-cost): True cost of hiring an employee including taxes and benefits
- [Startup Runway](https://www.stupidlyclever.com/startup-runway): How long until a startup runs out of cash given burn rate
- [ROAS Calculator](https://www.stupidlyclever.com/roas-calculator): Return on ad spend for any marketing channel
- [Engagement Rate](https://www.stupidlyclever.com/engagement-rate): Social media engagement rate by platform and follower count
- [Project Cost-Benefit](https://www.stupidlyclever.com/project-cost-benefit): Cost-benefit analysis with NPV and benefit-cost ratio
- [Price Indexation](https://www.stupidlyclever.com/price-indexation): Adjust contract prices for inflation using CPI or other indices

## Income & Wealth Comparisons

- [Income Percentile (Global)](https://www.stupidlyclever.com/income-percentile): Where does your income rank globally across all countries
- [Income Percentile (National)](https://www.stupidlyclever.com/national-income-percentile): Income percentile within a specific country
- [National Salary Percentile](https://www.stupidlyclever.com/national-salary-percentile): Salary rank within a country's workforce
- [Wealth Percentile](https://www.stupidlyclever.com/wealth-percentile): Net worth percentile globally and by country
- [Net Worth Calculator](https://www.stupidlyclever.com/net-worth): Calculate net worth and see how it compares
- [Lifetime Earnings](https://www.stupidlyclever.com/lifetime-earnings): Estimate total career earnings based on salary, growth, and years worked
- [Salary by Degree](https://www.stupidlyclever.com/salary-by-degree): Average earnings by educational qualification
- [Cross-Country Equivalent Salary](https://www.stupidlyclever.com/cross-country-equivalent-salary): Equivalent salary in another country adjusted for purchasing power
- [PPP Salary Converter](https://www.stupidlyclever.com/ppp-salary-converter): Convert salary between countries using purchasing power parity
- [Real Income Erosion](https://www.stupidlyclever.com/real-income-erosion): How much purchasing power a salary has lost to inflation over time
- [National Age Percentile](https://www.stupidlyclever.com/national-age-percentile): Age rank within the population of a given country
- [Global Age Percentile](https://www.stupidlyclever.com/global-age-percentile): Age rank within the global population

## Health Calculators

- [Longevity Calculator](https://www.stupidlyclever.com/longevity): Estimate life expectancy based on health and lifestyle factors
- [Biological Age](https://www.stupidlyclever.com/biological-age): Estimate biological age from health metrics
- [Heart Disease Risk](https://www.stupidlyclever.com/heart-disease-risk): 10-year cardiovascular risk using Framingham and SCORE2 models
- [Diabetes Risk](https://www.stupidlyclever.com/diabetes-risk): Type 2 diabetes risk using the FINDRISC questionnaire
- [Dementia Risk](https://www.stupidlyclever.com/dementia-risk): Estimated dementia risk based on lifestyle and health factors
- [Alcohol Impact](https://www.stupidlyclever.com/alcohol-impact): Effect of alcohol consumption on life expectancy and health
- [Survival Probability](https://www.stupidlyclever.com/survival-probability): Probability of surviving to a given age by country and sex
- [Due Date Calculator](https://www.stupidlyclever.com/due-date): Pregnancy due date and week-by-week milestones
- [Child Height Predictor](https://www.stupidlyclever.com/child-height): Predicted adult height for a child based on parental heights
- [Calorie Burn](https://www.stupidlyclever.com/calorie-burn): Calories burned by activity type, duration, and body weight
- [BMI Calculator](https://www.stupidlyclever.com/bmi): Body mass index with healthy range context
- [Body Composition](https://www.stupidlyclever.com/body-composition): Estimate body fat percentage and lean mass
- [Water Intake](https://www.stupidlyclever.com/water-intake): Daily water intake recommendation by weight and activity level
- [Sleep Cycle](https://www.stupidlyclever.com/sleep-cycle): Optimal wake times based on 90-minute sleep cycles
- [Diet Outcome](https://www.stupidlyclever.com/diet-outcome): Project weight change over time based on caloric deficit or surplus
- [Cohort Size](https://www.stupidlyclever.com/cohort-size): How many people of a given age are alive in a country
- [Lifetime Event Probability](https://www.stupidlyclever.com/lifetime-event): Probability of experiencing a life event (accident, illness, etc.)

## Global & Country Data

- [Country Affordability Match](https://www.stupidlyclever.com/country-affordability-match): Find countries that match your cost-of-living budget
- [Cross-Country Budget](https://www.stupidlyclever.com/cross-country-budget): Compare the true cost of living in two countries side by side
- [Climate Similarity Finder](https://www.stupidlyclever.com/climate-similarity-finder): Find countries or cities with a climate similar to your home
- [Country Retirement Fit](https://www.stupidlyclever.com/country-retirement-fit): Score countries for retirement suitability based on your priorities
- [Global Relocation Fit](https://www.stupidlyclever.com/global-relocation-fit): Rank countries for relocation based on lifestyle preferences
- [Cross-Border Retirement Income](https://www.stupidlyclever.com/cross-border-retirement-income): Retirement income comparison across countries
- [Country Safety Composite](https://www.stupidlyclever.com/country-safety-composite): Composite safety and stability score for countries
- [Air Quality Index](https://www.stupidlyclever.com/air-quality-index): Current and historical air quality data by city and country
- [Electricity Carbon Intensity](https://www.stupidlyclever.com/electricity-carbon-intensity): Carbon intensity of the electricity grid by country
- [Electricity Cost by Country](https://www.stupidlyclever.com/electricity-cost-by-country): Household electricity prices across countries
- [Carbon Footprint](https://www.stupidlyclever.com/carbon-footprint): Personal carbon footprint estimator by lifestyle choices
- [True Cost of Living](https://www.stupidlyclever.com/true-cost-of-living): Full cost-of-living comparison including hidden costs
- [Working Hours Comparison](https://www.stupidlyclever.com/working-hours-comparison): Average annual working hours by country

## Statistics & Probability

- [Confidence Interval](https://www.stupidlyclever.com/confidence-interval): Confidence interval calculator for proportions and means
- [Sample Size](https://www.stupidlyclever.com/sample-size): Required sample size using Cochran's formula
- [A/B Test Calculator](https://www.stupidlyclever.com/ab-test): Statistical significance for A/B test results
- [Bayes' Theorem](https://www.stupidlyclever.com/bayes-theorem): Calculate posterior probability using Bayes' theorem
- [Birthday Paradox](https://www.stupidlyclever.com/birthday-paradox): Probability that two people in a group share a birthday

## Physics & Engineering

- [Force, Mass & Acceleration](https://www.stupidlyclever.com/force-mass-acceleration): Newton's second law calculator — solve for F, m, or a
- [Electrical Power](https://www.stupidlyclever.com/electrical-power): Calculate power from voltage and current (P = IV)
- [Ohm's Law](https://www.stupidlyclever.com/ohms-law): Solve for voltage, current, or resistance using Ohm's law
- [Projectile Motion](https://www.stupidlyclever.com/projectile-motion): Range, time of flight, and max height for a projectile
- [Concrete Volume](https://www.stupidlyclever.com/concrete-volume): Calculate concrete volume for slabs, columns, and cylinders

## Energy & Home

- [EV vs Petrol Cost](https://www.stupidlyclever.com/ev-vs-petrol): Total cost of ownership comparison for electric vs petrol vehicles
- [Solar Savings](https://www.stupidlyclever.com/solar-savings): Estimated savings from solar panel installation
- [Solar Yield](https://www.stupidlyclever.com/solar-yield): Electricity output of a solar array by location and panel size
- [Home Electricity](https://www.stupidlyclever.com/home-electricity): Estimate household electricity consumption and cost
- [Generator Size](https://www.stupidlyclever.com/generator-size): Calculate the generator size needed for a home or site
- [Carbon-Optimised Lifestyle](https://www.stupidlyclever.com/carbon-optimised-lifestyle): Identify the highest-impact changes to reduce personal carbon footprint
- [Paint Coverage](https://www.stupidlyclever.com/paint-coverage): Calculate how much paint is needed for a room
- [Flooring & Tiling](https://www.stupidlyclever.com/flooring-tiling): Estimate materials and cost for floor or wall tiling

## Project Management Tools

- [Earned Value Management](https://www.stupidlyclever.com/earned-value-management): EVM metrics — CPI, SPI, EAC, and ETC
- [Earned Schedule](https://www.stupidlyclever.com/earned-schedule): Schedule performance using earned schedule methodology
- [PERT Estimating](https://www.stupidlyclever.com/pert-estimating): Three-point estimation using PERT formula
- [Risk Contingency](https://www.stupidlyclever.com/risk-contingency): Expected monetary value and contingency reserve calculator
- [Project Burn Rate](https://www.stupidlyclever.com/project-burn-rate): Budget consumption rate and runway for projects
- [Critical Path Method](https://www.stupidlyclever.com/critical-path-method): Identify the critical path in a project network diagram

## Personal Finance Decisions

- [Car Buy vs Lease](https://www.stupidlyclever.com/car-buy-vs-lease): True cost comparison of buying versus leasing a vehicle
- [Salary Negotiation Brief](https://www.stupidlyclever.com/salary-negotiation-brief): Data-backed salary negotiation guidance by role and location
- [Financial Life Position](https://www.stupidlyclever.com/financial-life-position): Overall financial health snapshot across savings, debt, and income
- [Health-Adjusted Retirement Horizon](https://www.stupidlyclever.com/health-adjusted-retirement-horizon): Retirement planning adjusted for personal health and longevity
- [Investment Quality Dashboard](https://www.stupidlyclever.com/investment-quality-dashboard): Score a stock across value, quality, and momentum factors
- [Running Pace Calculator](https://www.stupidlyclever.com/running-pace): Training paces for 5K, 10K, half marathon, and marathon

## Developer Tools

- [Validate Email](https://www.stupidlyclever.com/validate-email): Syntax and MX record validation for email addresses
- [Validate Phone](https://www.stupidlyclever.com/validate-phone): Validate and format phone numbers to E.164 standard
- [Validate VAT](https://www.stupidlyclever.com/validate-vat): Verify EU VAT numbers via the VIES service
- [Validate IBAN](https://www.stupidlyclever.com/validate-iban): IBAN checksum validation and bank identification
- [JWT Decode](https://www.stupidlyclever.com/jwt-decode): Decode and inspect JSON Web Token headers and payloads
- [Cron Parser](https://www.stupidlyclever.com/cron-parser): Parse and describe cron expressions in plain English
- [Encoding Tools](https://www.stupidlyclever.com/encoding-tools): Base64, URL encoding/decoding, and hash utilities
- [DNS Lookup](https://www.stupidlyclever.com/dns-lookup): Query DNS records (A, MX, TXT, CNAME, etc.) for any domain
- [SSL Checker](https://www.stupidlyclever.com/ssl-checker): Inspect SSL/TLS certificate details for any domain
- [Domain Age](https://www.stupidlyclever.com/domain-age): Find when a domain was first registered
- [IP Geolocation](https://www.stupidlyclever.com/ip-geolocation): Geographic location and ISP for an IP address
- [Password Generator](https://www.stupidlyclever.com/password-generator): Secure random password generator with configurable rules
- [Unit Converter](https://www.stupidlyclever.com/unit-converter): Convert between metric and imperial units across categories

## Example Queries for AI Agents

- "How many business days are there between two dates in Germany?"
- "Validate this phone number and return its E.164 format: +44 7911 123456"
- "What is the income percentile for a salary of $85,000 in Canada?"
- "Calculate the Altman Z-Score for a company with these financials..."
- "Find the top 5 countries with a climate similar to Lisbon"
- "What are the public holidays in Japan in 2027?"
- "Run a mortgage stress test: £400,000 property, £80,000 deposit, 6.5% rate"
- "What is the biological age implied by these health metrics?"
- "Calculate compound interest: $10,000 at 7% for 20 years"
- "What is the WACC for a company with 40% debt at 5% cost and 60% equity with beta 1.2?"
- "Price a bond: 5% coupon, 4.2% yield, 7 years to maturity, $1,000 face value"
- "What is the Kelly fraction for a bet with 55% win probability and 2:1 payoff?"

## Links

- Web calculators (free, no account required): [https://www.stupidlyclever.com](https://www.stupidlyclever.com)
- API documentation: [https://api.stupidlyclever.com/docs](https://api.stupidlyclever.com/docs)
- Sign up: [https://www.stupidlyclever.com/signup](https://www.stupidlyclever.com/signup)
- Support: [support@stupidlyclever.com](mailto:support@stupidlyclever.com)
- Terms: [https://www.stupidlyclever.com/terms](https://www.stupidlyclever.com/terms)
- Privacy: [https://www.stupidlyclever.com/privacy](https://www.stupidlyclever.com/privacy)