# Interest Calculator - Compound, Simple, Savings and Loan Payments

> Free online interest calculator: compound interest at any frequency with the effective annual rate, simple interest, monthly savings growth and loan payments.

- URL: https://qilingtools.com/en/math/interest
- Category: Math Tools (https://qilingtools.com/en/math)
- Tags: [Math](https://qilingtools.com/en/tags/math), [Finance](https://qilingtools.com/en/tags/finance)
- Last updated: 2026-10-26
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

Four everyday interest calculations: compound interest with six compounding frequencies (including continuous) and the effective annual rate, simple interest, the future value of a monthly savings plan, and the monthly payment on a loan compared against the equal-principal method.

## How to use

1. Choose compound, simple, regular savings or loan payment
2. Enter the principal, annual rate and term (or the monthly contribution and number of months)
3. Read the final amount, total interest or monthly payment

## Features

- Six compounding frequencies, continuous compounding included
- Effective annual rate (APY) for comparing offers
- Savings plans valued with the ordinary annuity formula
- Loan view shows the equal-instalment payment and the equal-principal first and last payments
- Interest difference between the two repayment methods

## FAQ

### What is the compound interest formula?

A = P(1 + r/n)^(nt) where P is the principal, r the annual rate, n the compounding periods per year and t the years; with continuous compounding A = P·e^(rt).

### Why does the effective annual rate matter?

It makes different compounding frequencies comparable: APY = (1 + r/n)ⁿ − 1. A nominal 3.5% compounded monthly yields slightly more than the same rate compounded annually.

### Equal instalments or equal principal?

Equal instalments keep the payment fixed and cost more interest overall; equal principal repays the same principal each month with falling interest, costing less in total but more up front. The tool shows the difference.

### Will my bank quote the same numbers?

The formulas match, but day-count conventions, rounding and early repayment can shift the figures by a few units — this tool is for estimating and comparing options.

### Can I see how the money grows year by year?

Yes. Use the plot link under the results: compound and simple interest are drawn against years, regular investing shows the monthly balance, and a loan shows the remaining principal — which makes it obvious how much of an early payment is interest.

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