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Interest Calculator

Updated 3 May 2026​
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​Our Simple Interest Calculator Makes the Numbers Clear
  • How much interest will you actually pay (or earn) on a fixed sum over a specific period? Our Simple Interest Calculator answers in seconds.
  • Simple interest applies the rate to your original principal only.
  • It does not compound, meaning interest does not earn interest on itself. This makes it the right calculation for short-term lending, court-awarded interest, IRD use of money interest, late payment charges, and some specific savings products.

If you are looking for compounding interest, please use our compound interest calculator

To use the calculator, enter:
  1. The principal amount - the sum being borrowed, owed, lent, or invested.
  2. The time period - in days, months, or years (use the toggle to switch units, and the value will convert automatically).
  3. The annual interest rate - the rate per year as a percentage. Your final interest will be calculated based on the actual time period you've entered, not a full year.

The calculator instantly shows three figures: The total interest accrued over the period, your daily interest rate (useful for working out interest on overdue payments), and the principal plus interest combined.

Simple Interest Calculator

Time period
Interest accrued $0.00
Principal + interest $0.00
Daily interest $0.00

Note: This calculator uses the simple interest formula (interest is not compounded). For savings, term deposits, or investments where interest earns interest over time, use our Compound Interest Calculator instead.

Important: Our calculations are based on the assumption that there is no change to the opening or closing balance (the 'amount') during the period ('days') interest is calculated. 
Christopher Walsh
MoneyHub Founder
Don't Overpay - Find the Best Personal Loan Rates with MoneyHub - Too Many Borrowers Get Ripped Off with a Personal Loan or Car Finance

Are you tired of overpaying with high interest rates and exorbitant fees? Our research shortlists three outstanding lenders known for their fair rates and reliable service:
Checking what interest rate you'll get is quick and easy - just a few minutes could save you thousands, given the range of interest rates. Remember
  • It's the interest rate you agree to now that makes a huge difference when you repay your loan week after week. We believe that signing up for finance with a car salesperson or via a bank is unlikely to be the cheapest option.
  • Advertising Disclosure: We may earn a commission from loans, but our top picks are always based on rigorous research and your best interest.
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