Methodology & data sources

Every calculator on DecisionsCalc is built the same way: a documented model, primary-source inputs, and a dated review trail. This page explains each model, names the sources behind the default figures, and describes how we keep them current. Nothing here is financial advice — see the full disclaimer.

How figures stay current

Every default value lives in a per-country data pack with a source and an “as of” date. An automated check fails our build when any live country's figures are more than 12 months old, so stale data cannot ship silently. The country stamp in the corner of each calculator shows exactly which country's figures you're seeing and when they were last reviewed. Where a country's localisation is still in progress, the stamp says so plainly — we show US-based figures with your local currency rather than pretending.

Who builds this — and how AI is used

DecisionsCalc is independently owner-operated and built with AI assistance. We say that plainly because trust here shouldn't rest on a byline — it rests on what you can check: every calculator's model is documented on this page, every default figure cites a primary source, every calculation is unit-tested, and an automated check blocks releases when any live country's figures are more than 12 months old. AI helps build and maintain the calculators and content; the owner reviews country data before it goes live, and the country stamp tells you honestly when a localisation is still in progress. DecisionsCalc is an independent publisher, not a regulated financial adviser. Corrections are welcome at [email protected]; data disputes are reviewed within two business days.

Per-calculator methodology

Assumptions that apply everywhere

Returns are treated as real (inflation-adjusted) unless a field says otherwise. Currency formatting follows the country you're viewing. Calculations run entirely in your browser — we never see, transmit, or store the numbers you enter. Defaults are sourced averages, not recommendations: the calculators exist so you can replace them with your own situation.