About thy.finance
thy.finance provides free, accurate financial calculators to help you make informed money decisions.
Our Mission
Help people understand their financial options through clear, reliable calculations. No signup required. No hidden fees. Just honest tools that work.
Why thy.finance?
Free Forever
No subscriptions. No ads. No catches. Financial planning tools should be accessible to everyone.
Privacy First
Your data never leaves your browser. We don't store, sell, or even see your information.
Thoroughly Tested
Over 1,000 automated tests ensure accuracy. Every calculator is validated against industry standards.
Open & Honest
See our methodology. Understand the math. No black boxes or hidden assumptions.
Our Calculators
We provide 28 financial calculators across 6 major categories:
Investment (5 calculators)
- Compound Interest - See how your money grows
- Investment Return - Calculate ROI on investments
- ROI Calculator - Evaluate investment performance
- Stock Profit - Calculate gains from stock trades
- Dividend Calculator - Plan dividend income with Monte Carlo simulation
Retirement (4 calculators)
- Retirement Calculator - Plan your retirement savings
- 401(k) Calculator - Maximize employer matches
- IRA Calculator - Traditional IRA planning
- Roth IRA Calculator - Tax-free retirement growth
Savings (3 calculators)
- Savings Goal - Reverse calculate monthly contributions
- Emergency Fund - Build your financial safety net
- Savings Interest - Simple interest calculations
Housing (4 calculators)
- Mortgage Calculator - Calculate home loan payments
- Mortgage Refinance - Evaluate refinancing options
- Rent vs Buy - Compare renting to buying
- Home Affordability - Find your price range
Loans (3 calculators)
- Auto Loan - Car payment calculations
- Debt Payoff - Snowball and avalanche strategies
- Credit Card Payoff - Escape high-interest debt
Business (4 calculators)
- Business Loan - Commercial loan analysis
- Break-Even - Find profitability threshold
- Profit Margin - Calculate business margins
- Cash Flow - Project business cash flow
Tools (5 calculators)
- Extra Payment Calculator - Pay off loans faster
- Refinance Analyzer - Compare refinancing scenarios
- Goal Planner - Reverse savings planning
- Scenario Comparison - Compare financial strategies
- Social Security Estimator - Estimate retirement benefits
Trust & Accuracy
Every calculator is validated with comprehensive automated tests:
- 580 validation tests - 20 per calculator covering edge cases and real scenarios
- 424 unit tests - Function-level testing for accuracy
- Black box testing - End-to-end user scenario validation
- Performance testing - Ensures fast, responsive calculations
- Python reference implementations - Independent verification
This level of testing is rare for financial calculators. We're confident in the accuracy of our tools.
Learn more about our testing methodology.
Why "thy.finance"?
The Story Behind Our Name
In a world of cold, corporate financial jargon, we wanted something different. Something personal. Something that speaks directly to you.
thy (pronoun, archaic)
belonging to or associated with the person being addressed; "your"
We chose "thy" because thy finances are deeply personal. Not "the market's" finances. Not "their" portfolio. Thy money. Thy goals. Thy future.
The word "thy" reminds us that every calculation, every number, every projection is about thy life, not abstract economics.
Our Philosophy: Finance for Thy Life
Financial planning isn't about complex formulas and intimidating spreadsheets. It's about:
💭 Thy Dreams
What do you want to achieve? Thy goals are unique to thee.
🛡️ Thy Security
How do you protect what matters? Build thy financial foundation.
✨ Thy Freedom
What does independence mean to thee? Define thy own path.
Master thy money, own thy future.
We believe financial tools should be personal, clear, empowering, and free.
That's why we're thy.finance — because this is about thy money, thy goals, thy future.
Last updated: October 2025