Michael

Builder and implementation

If our number doesn't match your lender's, your paycheck's, or your statement's - it's a bug, not a simplification.

Michael builds the calculators and the math behind them. With a background as a consultant turned builder, he owns the implementation side of PennyCalc - the formulas, the edge cases, and the methodology that keeps every tool consistent. He writes and maintains the debt payoff, auto loan, and mortgage-rate-history tools, the payroll and minimum-wage history pages, and the methodology page that documents how every rate and limit is sourced and verified.

His standard is that a calculator should match what the reader's own lender, paycheck, or statement will eventually show - if it does not, that is a bug, not a simplification. PennyCalc tools ship with the rounding rules the underlying authority actually uses (the IRS rounding on tax tables, the lender rounding on amortization, the BLS rounding on CPI) and the edge cases the reader actually hits (trade-in equity that exceeds the new-car price, prepayments mid-month, partial-year contributions). The hidden ones are documented in the methodology.

Michael's perspective is that most of the bad numbers on the internet are not malicious - they are someone who built a calculator in an afternoon, didn't model the edge case, and shipped it. The fix is patience: build the test fixture before the calculator, verify against the public source, then ship.

pages authored or co-authored

topic areas covered

Lender disclosures · IRS · FRED · BLS

primary sources

Test fixture first

build pattern

What Michael covers

Debt payoff toolsAuto loansMortgage rate historyMethodology documentationPayroll-tax implementation

My editorial standards

Match the authority's rounding. If the IRS rounds intermediate withholding figures to the nearest dollar at a specific step, PennyCalc does too. If the lender amortization rounds the monthly P&I and carries the rounding error into the next period, PennyCalc replicates that exactly. The output should match the reader's statement to the penny.
Model the edge case before the headline path. Most calculators handle the typical user; the design starts with the atypical user (negative trade-in equity, an extra principal payment in month one, a self-only HSA that switches to family mid-year) and lets the typical user fall out naturally.
Cite the source in the methodology page. Every rate, limit, schedule, or rule used anywhere on the site appears in the methodology page with its citation. If a fact isn't there, it doesn't ship.
Update the test fixtures when the underlying authority updates. New IRS Pub 15-T issued? The withholding tests get re-baselined before the calculator output changes. The order matters.
Document the rounding rule next to the formula. Inline. Not in a separate doc. The next maintainer reads the file, not the docs.

How I verify a fact before it ships

Lender-facing math (mortgage, auto, debt): replicated from the Truth-in-Lending disclosure formulas, cross-checked against a published lender's Loan Estimate sample.
Withholding math: IRS Publication 15-T, percentage method, current revision - tested against several known salary scenarios published in payroll-industry calculators.
Historical rate series (mortgage, auto, payroll): FRED series ID specified in the methodology, refreshed annually.
Minimum wage and payroll-tax-rate history: Department of Labor and SSA primary sources, cross-checked against the BLS handbook tables.

Signature work

Methodology

The single document that lists every rate, limit, and formula used anywhere on PennyCalc with its source and the date it was last verified. The page that proves the site is built honestly.

Auto Loan Calculator

Handles trade-in equity (positive and negative) correctly, models the actual sales-tax-on-trade-difference rules state by state, and breaks down the total interest by year. Pairs with the auto loan rate history page.

Debt Payoff Calculator

The avalanche-vs-snowball comparison that runs both strategies in parallel against the same debt portfolio and shows the actual interest-paid difference. The right answer is usually whichever the reader will actually stick with.

Federal Minimum Wage History (1938-2026)

The long-form historical reference with the legislative context, currently one of the higher-cited PennyCalc pages in Microsoft Copilot grounding queries.

Working with the team

Michael's role is the receiving end of Josh's spreadsheets and the supplying end of Jessie's editorial. Josh builds the math in a spreadsheet, Michael implements it in code with the test fixtures, then Jessie writes the editorial layer that explains what the user is looking at. The methodology page is the shared artifact - every team member can point at it, every reader can audit against it.

What I'm working on now

Currently expanding the test-fixture coverage for the state paycheck calculators, which is the highest-edge-case-density part of the site. After that, building the federal funds rate history reference, which Josh has been requesting as a cross-link for the mortgage rate pages.

Spotted an error?

A mismatch with what your lender or paycheck actually shows is the highest-priority bug class on the site. Fastest path: [email protected], subject line "Michael / [page URL]" with a one-line description of what number didn't match and what the authoritative source shows. You'll get a fix, usually within a day.

PennyCalc is a team of data people who build the financial tools they use themselves. Read more about how we work on the about page and how we source every figure in our methodology.