Search for “mortgage calculator” and the first results are Bankrate and NerdWallet. Both will give you a calculator. Both will also surround it with affiliate links to mortgage lenders, credit card offers, and insurance products. The calculator is not the product. You are the product. The calculator exists to put you in a buying mindset so that the affiliate links convert.
This is the business model behind virtually every financial calculator on the web. The computation is free because the real revenue comes from steering your financial decisions toward products that pay the site a commission. The tools work. The advice is biased. And most users do not realize the difference.
I built Calculators.money because financial literacy tools should not come with an agenda. It has 357 calculators across 23 categories, a 444-term glossary, and country-specific tools for the US, UK, Canada, and Australia. No affiliate links. No product recommendations. No financial incentive to steer you toward one decision over another. Every calculation runs in the browser and no financial data ever leaves your device.
The long tail of financial decisions nobody builds for#
The major financial sites build calculators for the decisions that generate commissions: mortgages, credit cards, insurance, personal loans. Those are the calculators that funnel into product recommendations. The long tail of financial decisions — the ones that do not lead to a sale — gets ignored.
I built for the long tail. A freelancer figuring out their hourly rate. A small business owner checking days sales outstanding or estimating cash runway. A couple deciding whether to pay cash or finance a purchase. A parent estimating the cost of raising a child. Someone checking whether their subscription spending has crept beyond what they intended.
These are real financial decisions that people face constantly, and the web offers almost nothing for them because there is no affiliate commission at the end. A sinking fund calculator does not generate mortgage leads. A lifestyle creep calculator does not sell credit cards. A pet cost calculator does not convert into insurance revenue. So nobody builds them — unless building them is the point.
Institutional-grade tools that should not be locked behind paywalls#
I deliberately built tools that are normally available only through professional software or brokerage platforms. The options suite includes 15 calculators: Black-Scholes pricing, Options Greeks, implied volatility, IV Rank and Percentile, probability of profit, covered call analysis, and options payoff diagrams. This level of options analysis is typically locked behind a brokerage account or a paid subscription to a platform like OptionStrat or Thinkorswim.
The portfolio analytics suite has 26 tools: Efficient Frontier visualization, Risk Parity, Minimum Variance Portfolio, Value at Risk, correlation stress testing, Jensen’s Alpha, Sharpe and Sortino ratios, maximum drawdown, and risk contribution analysis. These are tools that institutional portfolio managers use daily. A retail investor with a self-directed account has just as much need for them but historically no access without expensive software.
Making these tools available to anyone with a browser is a deliberate act of democratization. If a twenty-two-year-old is going to trade options — and the apps have made sure they will — they should at least be able to calculate the Greeks and understand the probability of profit before they enter a position.
Financial calculations deserve mathematical precision#
One technical decision I am particularly deliberate about: I built the entire platform on decimal.js, an arbitrary-precision decimal library, instead of using JavaScript’s native floating-point arithmetic. This matters for financial calculations. Standard JavaScript floating-point math produces rounding artifacts — the classic example is that 0.1 + 0.2 equals 0.30000000000000004, not 0.3. In a compound interest calculator or a loan amortization schedule, those tiny errors compound across hundreds of calculation steps and produce results that are subtly wrong.
Most financial calculator websites use standard JavaScript math because it is simpler and the errors are small enough that most users will not notice. I use decimal.js because financial calculations should be correct, not approximately correct. This is the kind of engineering decision that is invisible to the user but matters if you care about the accuracy of the tools you build.
Four countries, 23 categories, one privacy guarantee#
Financial systems are national. A mortgage calculator that only understands American conventions is useless to someone in the UK dealing with Stamp Duty or in Canada calculating CMHC insurance. I built country-specific tools for the four major English-speaking financial markets: the US (401(k), Social Security, Roth IRA), Canada (RRSP, TFSA, FHSA, CPP), the UK (ISA, SIPP, UK State Pension), and Australia (Superannuation, FHSS, franking credits).
Every one of the 357 calculators runs client-side. Financial data — income, debts, portfolio values, tax situations — is among the most sensitive personal information people have. It should never leave the device. This is the same client-side architecture I use across PDF Pony, ImageNurse, GIS Tools, Statistics Tools, and MyText. The principle is consistent: if the browser can do the computation, the server should not touch the data.
AI made 357 calculators possible#
Building 357 financial calculators as a solo developer — each with educational content, real-world scenarios, preset examples, and cross-references — would not have been feasible without AI-assisted development. I used the same Claude Code workflow I have refined across my other tool platforms: describe the calculator’s behavior, review the output, test against known scenarios, refine.
AI was particularly valuable for the educational content on each tool. Every calculator includes methodology explanations, common mistakes, and guidance on interpretation. Producing that content at scale across 357 tools — while maintaining accuracy on topics ranging from Black-Scholes option pricing to Australian franking credits — required AI to handle both the volume of implementation and the depth of educational content.
Calculators.money runs entirely in the browser, works offline, and is available in three languages.
