About Compoundly

Most calculators answer a single question and hand back a single number. Compoundly is built as a simulator instead: you change an input, and the curve, the totals, the schedule and the milestones all move together, because they are all read from the same run.

The debt side gets exactly as much attention as the investment side. Amortisation, minimum payments, overpayments, refinancing and payoff ordering are first-class tools, not an afterthought bolted onto a savings calculator.

• “I can actually see when compounding starts doing most of the work.”
• “I finally understand why this loan costs so much — and what an extra payment really changes.”

• Purpose-built calculation engines with a test suite covering zero and negative rates, payments below the interest charge, negative amortisation, minimum-payment rules and long horizons.
• Charts drawn as hand-written SVG, so every curve, band and marker is under direct control.
• Desktop and mobile layouts that rearrange the interface rather than shrinking it.
• Colour is never the only signal: line style, pattern, glyph and label carry the same information.
• Full keyboard operation, screen-reader summaries and a text equivalent of every chart.
• Reduced-motion preferences are respected throughout.

The complete calculation model is documented on the methodology page, including its known limitations.

Compoundly does not tell you what to do with your money. It does not call one repayment ordering better than another, it does not tell you whether to invest or repay, and it does not use alarming language about debt. It shows what the arithmetic produces from the assumptions you entered, states those assumptions plainly, and leaves the decision with you.

It is not investment, lending, credit, tax or debt advice, and it is not a replacement for your lender's statements.