METHODOLOGY
Every result should be reproducible. This page explains the calculation rules shared across Compound Planner.
APY is converted to an effective monthly rate with (1 + APY)^(1/12) − 1. Nominal APR uses the selected compounding cadence. Contributions are placed on the selected schedule; weekly and biweekly amounts are distributed evenly across months.
Credit card and debt tools divide APR by 12, add interest before the end-of-month payment, and roll freed minimum payments into the next target. Real card issuers may accrue interest daily and apply fees or changing rates.
Internal calculations use full JavaScript floating-point precision. Displayed amounts are rounded for readability. Projections are limited to 100 years and extreme inputs are bounded to keep the browser responsive.
Formula tests cover APY/APR conversion, recurring savings, simple versus compound interest, investment fees, credit card amortization, and snowball versus avalanche ordering. Before publishing, the full site must build successfully and all automated tests must pass.
Definitions and consumer guidance are checked against Investor.gov, the U.S. Consumer Financial Protection Bureau, and the Federal Deposit Insurance Corporation. Product-specific terms from a bank or card issuer always take precedence over this estimate.