Monthly Interest Calculator (with Examples and Formula)

This online calculator computes the interest accrued monthly on an amount of borrowed money.


  • Principal or Initial Loan amount in any currency
  • Annual Percentage Rate (APR) or Interest Rate
  • Number of days in the month (28, 29, 30 or 31)

The calculator will provide the following interest numbers: daily rate (%), daily amount and total amount over the month (in any currency).


Daily Periodic Rate = APR/365

Daily Interest = Current Balance × Daily Periodic Rate

Total Interest = Principal × (1 + Daily Interest Rate)N – Principal

where N is the number of days in a month

Example Calculation

A principal amount of $5000 at an APR of 5% gives a monthly interest of $20.59.


A Monthly Interest Calculator is a tool designed to help you determine how much interest accrues on a balance over a month. This can be particularly useful for managing monthly loan payments, understanding the growth of investments, or calculating interest on savings.

What is Monthly Interest?

Monthly interest refers to the amount of interest that accrues on a principal balance over the course of a month. This can apply to various financial products, including:

  • Loans: Most personal, auto, and home loans calculate interest monthly.
  • Mortgages: Mortgage interest is typically calculated and added to the principal balance on a monthly basis.
  • Savings Accounts: Some savings accounts and certificates of deposit (CDs) accrue interest monthly.
  • Credit Cards: While credit cards often calculate interest daily, they commonly report and apply interest charges monthly.