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Interest Rate Calculator

The rate implied by an amount, a payment and a term.

Calculators Reviews Free · no sign-up
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CompoundingNominal rateEffective annual rate

Annual interest rate

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Rate per period—
Nominal annual rate—
Effective annual rate—
Total repaid—
Total interest—
Interest as % of principal—

Quick Tool Overview

The Interest Rate Calculator recovers the rate from a deal that never stated one — a payment schedule, a total repayable, or a starting and ending value. It reports the periodic, nominal and effective annual rates, which are three different numbers.

What it does
Finds the interest rate implied by the other loan or investment terms
You give it
An amount and payment, or a start and end value over a period
You get back
The periodic rate, nominal annual rate and effective annual rate
Best for
Pricing an offer that quotes a payment but no percentage
Calculators Free, unlimited use No sign-up Runs in your browser

About the Interest Rate Calculator

Sometimes you know everything about a deal except the rate. A finance offer quotes a monthly payment and a term but no percentage; an investment doubled over a period; a store credit plan states only the total repayable. This calculator recovers the rate from those.

It matters because an unstated rate is usually an unflattering one. Convert a payment schedule into a percentage and offers that looked reasonable often turn out not to be, particularly on short terms where a modest-looking fee annualises into a very large number. The calculator also converts between nominal and effective annual rates, which is the other common source of confusion when two quotes use different compounding frequencies.

Key features of the Interest Rate Calculator

Unstated rates recovered

A finance offer with a monthly payment and no percentage can be converted into one, and it is usually unflattering.

Nominal and effective both shown

Twelve percent compounded monthly is an effective 12.68, and only one of those is comparable across offers.

Two input modes

Work from a payment schedule, or from two values and a time period for a growth rate.

Short-term annualisation

A small fee over a short term annualises into a very large rate, which is exactly what needs to be visible.

Solved numerically

Iterative solution, because the rate cannot be isolated algebraically when payments are involved.

How to use the Interest Rate Calculator

  1. 1

    Choose your inputs

    Work from a loan and payment, or from a starting and ending value over a period.

  2. 2

    Enter the known figures

    The amount, the regular payment and the number of periods, or the two values and the time.

  3. 3

    Read the rate

    The periodic rate, the nominal annual rate and the effective annual rate are all shown.

  4. 4

    Compare like with like

    Use the effective annual rate when comparing offers with different compounding frequencies.

Frequently asked questions

From the amount borrowed, the payment and the number of payments. The equation cannot be rearranged for the rate directly, so it is solved by iteration, which is what this calculator does.

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