About these calculators

Why they exist

One of the things I said I’d do on debit-is-left.com is build tools that save time. These are those tools: 38 calculators for loans, depreciation, pricing, taxes, and pay.

Most calculator sites give you a number and no way to check it. So every calculator here shows its work — the formula, a worked example, the assumptions — and hands you a spreadsheet that does the same math with real formulas.

What you get with each one

• The answer, plus the steps behind it, worked by the calculator itself.
• An Excel workbook with live formulas: yellow input cells you can change, a Read Me, and the assumptions and sources the math relies on.
• The mistakes I see most often, and answers to the questions people ask.
• A reviewed date and version number, so you know how current it is.

Who they're for

Small-business owners and freelancers figuring out pricing, payroll, and taxes. Bookkeepers and accountants who want a quick schedule they can drop into a workpaper. Employees checking a paycheck or comparing offers. Students who want to see the formulas actually work.

What they're not

They’re not tax or legal advice, and they don’t know your whole situation. They’re the math, done carefully, with the assumptions written down. For the big decisions, take the spreadsheet to a professional — that’s part of why it exists. The disclaimer has the formal version.

Your numbers stay with you

Everything runs in your browser, including building the Excel file. There are no accounts, and nothing you type is sent anywhere. Privacy details.

Found a mistake?

I’d genuinely like to know. Tell me what looks off, and I’ll fix it, bump the calculator’s version, and note it in the changelog. How the math is built and tested is on the methodology page.

More from Ben

New here? Start Here on the main site, browse the notes, or read the About page.