A feature filled WordPress interest calculator

Converting APR to monthly repayments

According to Wikipedia: The term annual percentage rate of charge (APR), corresponding sometimes to a nominal APR and sometimes to an effective APR (or EAPR), describes the interest rate for a whole year (annualized), rather than just a monthly fee/rate, as applied on a loan, mortgage loan, credit card, etc.


Effective APR

The plugin uses Effective APR by default. If you want monthly or some other period of repayment you need to calculate the interest rate for the repayment period.

This is the formula for Effective APR:

r = (1 + i)1/n – 1


r = rate per period
i = annual interest eg: 8% is 0.08
n = number of payments in a year


With 14.9% interest per year with monthly payments the rate is:

r = (1 + 0.149) 1/12 – 1

r = (1.149) 0.8333333 – 1

r = 1.01164 – 1

r = 0.01164

r = 1.164%

All very simple and can be used for weekly or even daily repayments in most of the world.

Nominal APR

If you are in the USA and want to use nominal APR the formula is:

r = (1 + i) / n


r = rate per period
i = annual interest
n = number of payments in a year


Given 14.9% interest per year with monthly payments the rate is:

r = 14.9 / 12

r = 1.2141%

Once you have the interest rate for the repayment period you can plug it into the amortization formula.

  1. Kamran on 28 May 2022:

    Can I change APR to a custom tab? I want to user will input interest rate manually

    Reply to Kamran

    • Graham on 28 May 2022:

      Hi Kamran,
      If you have upgraded there is an option to display and interest rate slider. You also have the option to display input fields instead of sliders. If you just want an input field for the interest rate it’s not an option with this plugin. But you could get a custom version built for about the same cost as the upgrade.

      Reply to Graham

  2. ghazale on 16 May 2022:

    what is secondary rate?

    Reply to ghazale

    • Graham on 16 May 2022:

      You have have different interest rates depending on the principal or term. For examples 2% for loans under £1000 and 3% for loans above £1000.

      Reply to Graham

  3. MOMO on 27 Jan 2021:

    I can’t find the APR in my setting. I don’t know why! but I ‘m sure APR is not appeared in the settting. because of this my interest setting is wrong. please help . just know I’m using pro version

    Reply to MOMO

    • Graham on 27 Jan 2021:

      Hi Momo,

      Your APR is the primary interest rate. All the interest rates are APR by default.

      Reply to Graham

Reply to Graham

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The plugin is ideal for finance calculations, payday loans, fixed fee payments, regular payments, savings, comparisons, foreign exchange and pretty much anything else that gets calculated from a variable amount.

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