# calculatorapp.io
> A mobile-friendly collection of 101 free calculators and tools across finance, income, health, lifestyle, cooking, math, AI, and browser utilities — cross-platform, instant results, no sign-up required.

## Author
- [Alex Doyle](https://calculatorapp.io/authors/alex-doyle.html): Personal finance and technology writer. 44 guides covering mortgages, tax math, calorie science, AI cost analysis, and more.

## Top Calculators

### Financial
- [Mortgage Calculator](https://calculatorapp.io/financial/mortgage.html): Monthly payment, amortization table, LTV ratio, PMI warning. Uses standard P&I amortization formula.
- [Compound Interest Calculator](https://calculatorapp.io/financial/compound-interest.html): Investment growth over time with optional monthly contributions and visual chart.
- [Home Affordability Calculator](https://calculatorapp.io/financial/home-affordability.html): How much house you can afford using the 28/36 debt-to-income rule.
- [VA Disability Calculator](https://calculatorapp.io/financial/va-disability.html): Combined VA disability rating and monthly tax-free compensation using the VA whole-person method.
- [Debt Payoff Calculator](https://calculatorapp.io/financial/debt-payoff.html): Avalanche vs snowball method compared side by side.
- [Retirement Calculator](https://calculatorapp.io/financial/retirement.html): Retirement savings projection using the 4% rule.
- [Rent vs Buy Calculator](https://calculatorapp.io/financial/rent-vs-buy.html): Break-even analysis for renting vs buying a home.

### Income & Tax
- [Tax Bracket Calculator 2026](https://calculatorapp.io/income/tax-bracket.html): Federal income tax bracket, effective rate, and exact taxes owed with full bracket breakdown.
- [1099 vs W2 Calculator](https://calculatorapp.io/income/1099-vs-w2.html): True take-home comparison for contractors vs employees including self-employment tax.
- [After-Tax Paycheck Calculator](https://calculatorapp.io/income/paycheck-after-tax.html): Exact take-home pay after federal, state, FICA, and pre-tax deductions.

### Health
- [BMI Calculator](https://calculatorapp.io/health/bmi.html): Body Mass Index using WHO/CDC standards with visual scale and healthy weight range.
- [Calorie Calculator](https://calculatorapp.io/health/calorie.html): BMR and TDEE using the Mifflin-St Jeor equation. Daily calorie targets for weight loss, maintenance, or gain.
- [Pregnancy Calculator](https://calculatorapp.io/health/pregnancy.html): Due date, current week, trimester, and key milestones from LMP or conception date.
- [Ideal Weight Calculator](https://calculatorapp.io/health/ideal-weight.html): Healthy weight range using 5 scientific formulas: Hamwi, Devine, Robinson, Miller, and BMI range.

### AI Tools
- [AI API Cost Calculator](https://calculatorapp.io/ai/api-cost-calculator.html): Compare API costs across Claude Opus/Sonnet/Haiku, GPT-5.4/mini/nano, and Gemini 3.1 Pro/Flash — input/output token pricing with monthly volume modeling.
- [Token Utilization Calculator](https://calculatorapp.io/ai/token-calculator.html): Estimate token count and context window usage across Claude, GPT, and Gemini models.
- [RAG Pipeline Cost Calculator](https://calculatorapp.io/ai/rag-pipeline-cost.html): Full cost breakdown for RAG systems: embedding, vector DB, retrieval, reranking, and LLM inference per query.
- [LLM Margin Calculator](https://calculatorapp.io/ai/llm-margin.html): Gross margin, break-even price per query, and pricing sensitivity for AI-powered products.
- [AI ROI Calculator](https://calculatorapp.io/ai/ai-roi.html): Return on investment for AI implementations — labor savings, productivity gains, payback period.
- [AI Subscription ROI Calculator](https://calculatorapp.io/ai/ai-subscription-roi.html): Is ChatGPT Plus, Claude Pro, or Copilot worth it? ROI based on your hourly rate and time saved.

### Cooking
- [Recipe Scaling Calculator](https://calculatorapp.io/cooking/recipe-scaling.html): Scale any recipe up or down. Outputs clean cooking fractions, not decimals.
- [Cooking Measurement Converter](https://calculatorapp.io/cooking/cooking-measurement-converter.html): Cups to grams, tablespoons to ml — ingredient-specific conversions for 40+ foods.
- [Coffee Ratio Calculator](https://calculatorapp.io/cooking/coffee-ratio.html): Perfect coffee-to-water ratio for pour over, French press, espresso, and cold brew.

### Math & Utility
- [Percentage Calculator](https://calculatorapp.io/math/percentage.html): Three modes — find X% of Y, what percent X is of Y, and percentage change.
- [Age Calculator](https://calculatorapp.io/math/age-calculator.html): Exact age in years, months, and days. Zodiac sign included.
- [Time Zone Calculator](https://calculatorapp.io/math/timezone.html): Convert times between 40+ time zones with live world clock and DST-aware conversions.
- [Square Footage Calculator](https://calculatorapp.io/math/square-footage.html): Room and floor plan area calculation.

## Blog Guides
- [How to Calculate Your Monthly Mortgage Payment](https://calculatorapp.io/blog/how-to-calculate-mortgage-payment.html): P&I formula, PITI breakdown, PMI, 15 vs 30-year comparison.
- [What Is BMI and How Is It Calculated?](https://calculatorapp.io/blog/what-is-bmi.html): WHO/CDC standards, limitations, healthy ranges.
- [Compound Interest Explained](https://calculatorapp.io/blog/compound-interest-guide.html): Formula, real examples, effect of contribution frequency.
- [1099 vs W2: The True Cost Comparison](https://calculatorapp.io/blog/1099-vs-w2-true-cost.html): Self-employment tax, benefits gap, real take-home math.
- [How Many Calories Per Day?](https://calculatorapp.io/blog/how-many-calories-per-day.html): Mifflin-St Jeor equation, TDEE, activity multipliers.
- [House Hacking Guide](https://calculatorapp.io/blog/house-hacking-guide.html): Strategy, numbers, and calculator walkthrough.
- [VA Disability Combined Rating Guide](https://calculatorapp.io/blog/va-disability-combined-rating.html): Whole-person method explained step by step.
- [AI API Cost Comparison 2026](https://calculatorapp.io/blog/ai-api-cost-comparison.html): Claude vs GPT-5.4 vs Gemini 3.1 — full cost breakdown by use case and scale.
- [AI ROI and Workforce Replacement Guide](https://calculatorapp.io/blog/ai-roi-workforce-replacement-llm-guide.html): Real ROI math (757% year-1 worked example), which jobs are being replaced now, and hidden implementation costs.
- [Is ChatGPT Plus Worth It in 2026?](https://calculatorapp.io/blog/is-chatgpt-plus-worth-it.html): Break-even math at every hourly rate, Free vs Plus feature comparison, $0.91/workday analysis.

## About
- Site: https://calculatorapp.io
- Contact: hello@calculatorapp.io
- Privacy Policy: https://calculatorapp.io/privacy-policy.html
- All tools are free, no sign-up required, browser-based only.