A growing set of single-page tools for the figures behind housing and household costs — mortgage repayments, rate changes, utility splits, and similar maths you want to sanity-check yourself. Each tool runs in your browser, cites its sources, and lives on its own subdomain.
Tools
Compare the water charges in your 2025/26 council rates with your first 2026/27 Tiaki Wai invoice — then see how your increase lines up with the figures Tiaki Wai published.
water.runthenumbers.org.nzMortgage scenarios, interest and fee comparisons, and other household calculations will be added here as they ship — same one-page format, same browser-first approach.
Coming laterAbout this collection
Run the Numbers is not a bank app or a signed-in dashboard. Each calculator is a standalone page — inputs in, working shown, assumptions spelled out — so you can bookmark the exact scenario you care about.
Tools that use your files or figures process them on your device unless the page says otherwise. Formulas, defaults, and links to official data sit on each tool’s page.