About these interest tools

This site provides working tools for interest totals across fixed-rate loan periods, a loan's full schedule, a selected loan year, savings growth, and a simplified credit card payoff model. The homepage tool separates cumulative interest from cumulative principal paid.

How results are computed

Calculations run in your browser using the values you enter. Fixed-rate loan tools build a constant-payment schedule and sum the interest and principal portions in an inclusive payment range. Savings growth compounds a single starting deposit. The credit card tool applies a daily compounding rate over equal monthly periods and subtracts a fixed payment.

Intermediate values retain full precision; displayed dollar values are rounded. A lender or account provider may use daily accrual, transaction dates, rounded payments, or other terms that differ from the models. Each tool states its assumptions and links to the method it uses.

Source policy

Microsoft documents its financial functions and worked example inputs. The CFPB explains amortization and credit card daily rates. SEC Investor.gov defines compound interest and provides a public calculator. SEC classroom material supplies the savings example inputs and explains how annual compounding works. These examples are not current lending or deposit offers.

Source documentation checked on 2026-10-05. No changing market-rate dataset is used. See the disclaimer for the scope of the calculations and privacy information for how inputs are handled.