# How the Mortgage Penalty Calculator Works

> Three months’ interest versus IRD, both industry comparison-rate methods, and how to read a lender payout statement.

Category: Calculator Guide
Last verified: 2026-09-12
Source: https://ratellow.com/mortgages/penalty-calculator/guide

## TL;DR
- Ask which comparison rate and which remaining-term bucket the payout statement used, then rerun those inputs on the parent tool.
- The posted-rate method is the expensive one only when the origination discount is deeper than today’s posted-to-market spread.
- Worked examples stay on the parent calculator; this guide is the payout-statement checklist.