Small calculators for expensive decisions

One tool so far, built to be honest about what it does not know. No accounts, no paywall, and no calculator input ever leaves your browser.

Every tool here follows the same rules: the formula is published, the defaults are labelled as placeholders, and the page says what it leaves out.

Why so few tools

Because most calculators on the internet exist to capture a search query, not to answer a question. They ship a form, hide the maths, and fill the page with words. This site would rather ship one page whose output you can verify by hand.

What is coming next

More ownership maths: total cost of keeping a device, break-even for repairs versus replacement, and cost-per-year comparisons across categories. Each one gets published only when the formula can be stated in two lines.