Writing
Verified computation, argued in public
The reasoning behind the product, held to the product’s own bar: primary-source citations, no invented statistics, and every claim about a model traceable to its published spec. When a constant appears, the facts registry owns it.
Foundations
The Verified-Computation Manifesto
Financial software has been graded on whether the number looks right. That is no longer enough.
Foundations · By Worthune Staff
Calculator, Model, Engine, Spec: A Working Vocabulary
Four words the industry uses interchangeably. We use them precisely, and here is the difference.
Foundations · By Worthune Staff
Six Answers a Financial UI Should Be Able to Give
Six artifacts, one question. If your product cannot produce all six on demand, the number is a claim, not a computation.
Foundations · By Worthune Staff
Table Stakes vs. Moat: Deciding What to Build In-House
Eight questions. Answer honestly. The scoring tells you whether the calculator is your differentiator or your plumbing.
Foundations · By Worthune Staff
The Hidden Cost of a Simple Retirement Calculator
The formula fits on a napkin. The edge cases do not.
Foundations · By Worthune Staff
Approximation vs. Computation: Why LLMs Should Not Do Your Arithmetic
Language models predict the next token. Your users assume the number is exact. That gap is the whole problem.
Foundations · By Worthune Staff
The Glass Box Principle
Black box means the answer is closed. Glass box means every claim is a link.
Foundations · By Worthune Staff
Financial Trust Signals, Ranked
Twelve signals users, regulators, and reviewers actually check. Not all twelve carry the same weight.
Foundations · By Worthune Staff
Buy-vs-Build Worksheet for Financial Calculators
A dollarized comparison. Bring your fully-loaded engineer cost and be honest about the maintenance calendar.
Foundations · By Worthune Staff
A Short History of Building Calculators In-House
Every generation of financial software rebuilds the same calculators. Here is the pattern, and where it breaks.
Foundations · By Worthune Staff
Model catalog
Refinance Break-Even, Explained From the Spec
Seven inputs, one deliberately narrow question: does the rate drop pay for its closing costs before you move?
Model catalog · By Worthune Staff
The FIRE Model: What Financial Independence Actually Means in Code
A withdrawal rate, a target multiple, and a spec that says what the model does not attempt.
Model catalog · By Worthune Staff
Social Security Timing: Three Claiming Ages, Honestly Compared
The model compares claiming at 62, at full retirement age, and at 70 — with the discounting stated, the formulas published, and the exclusions named.
Model catalog · By Worthune Staff
Rent vs. Buy Is a Net-Worth Race, and the Model Runs It Openly
Not a monthly-payment comparison. Two balance sheets, one year at a time, with the finish line published.
Model catalog · By Worthune Staff
The Loans & Credit Pack: Eight Models and the Cent That Mattered
Eight loan decisions, one verification bar — and a rounding convention that exists because an adversarial review found the bug before any user could.
Model catalog · By Worthune Staff
Equity Compensation: Three Models, Scoped to What Ships
RSU diversification, ESPP participation, and mega-backdoor Roth capacity — with the boundaries stated before the arithmetic.
Model catalog · By Worthune Staff
Roth vs. Traditional: A Break-Even Model, Not an Opinion
The comparison is a marginal-rate crossover. Framing it as opinion is how the industry has kept the question fuzzy for decades.
Model catalog · By Worthune Staff
Long-Term Care: Insure or Self-Insure, With the Assumptions Visible
The model does not price a policy. It compares a policy you have been quoted against carrying the risk yourself — which is the decision people actually face.
Model catalog · By Worthune Staff
The Emergency Fund Model Solves for Time, Not Guilt
Given what you can actually save each month, when does the buffer exist? That is the question the model answers — the other direction produces numbers people ignore.
Model catalog · By Worthune Staff
HSA Contribution Limits, Registry Facts, and the Model on the Roadmap
HSA contribution limits are in the registry today. The projection model is not. This is the piece to read before either is confused for the other.
Model catalog · By Worthune Staff
Comparisons
Verified-Model API vs. Homegrown Calculator
Six dimensions to compare on. The comparison is not about the arithmetic; it is about everything that has to be true around the arithmetic.
Comparisons · By Worthune Staff
Embed Widgets vs. Backend API vs. MCP
Three patterns for putting verified math on a product surface. The right one is the one that matches the surface.
Comparisons · By Worthune Staff
Deterministic Models vs. LLM-Generated Math
Two ways to produce a number for a user. One is arithmetic. The other is prediction. The right products use both.
Comparisons · By Worthune Staff
Static Content Calculators vs. Live-Constants Calculators
A number a page displays is either bound to a source that updates or it is drifting. The gap between the two widens every revision cycle.
Comparisons · By Worthune Staff
Open-Source Financial Libraries vs. a Maintained Registry
Both are valid choices. The comparison is about who owns the maintenance calendar, not about which is philosophically purer.
Comparisons · By Worthune Staff
White-Label Planning Suites vs. Composable Models
The all-in-one gives you a full UI. The composable gives you a catalog. Both are legitimate; the choice is about who owns the top layer.
Comparisons · By Worthune Staff
Powered-by Attribution vs. White-Label: A Cost Tradeoff
A visible attribution is a real cost to some brands and a real benefit to others. The comparison is about who the end user is and what they should see.
Comparisons · By Worthune Staff
Compliance-Owned Copy vs. Model-Cited Answers
Two ways to defend a number in front of a customer. The comparison is about which artifact carries the weight.
Comparisons · By Worthune Staff
US vs. Global Financial Calculators: Why This Product Starts Domestic
The regulatory surface, the constant registries, and the data quality across jurisdictions are not close to equivalent. Starting domestic is a scope discipline, not a limitation.
Comparisons · By Worthune Staff
Freemium APIs in Fintech: What Free-With-Attribution Actually Means
Free-tier posture varies wildly across the market. The comparison is between how durably each vendor commits to what free means today.
Comparisons · By Worthune Staff