Simple Interest Calculator

Calculate simple interest and the total amount payable or receivable, with the formula worked out.

FreeNo sign-upRuns in your browserMobile-friendly

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What does the Simple Interest Calculator do?

Simple interest is charged only on the original principal: SI = P × R × T, where R is the annual rate and T the time in years. It is used for some short-term loans, informal lending and many textbook problems.

Enter time in years, months or days (days use a 365-day year). The calculator also shows interest per year and per month.

How to use the Simple Interest Calculator

  1. Enter the principal.
  2. Enter the annual rate.
  3. Enter the time and choose its unit.
  4. Read the interest and total amount.

Examples

Classroom problem

P = 50,000, R = 8%, T = 3 years → SI = 12,000; total 62,000.

Short loan

20,000 at 12% for 90 days → about 591.78.

Common use cases

  • Maths and finance homework
  • Short-term personal loans
  • Comparing with compound interest

Features and benefits

  • Private by design — your data is processed on your device and never uploaded.
  • Free with no account, no watermark and no usage limits.
  • Works on phones, tablets and desktops in any modern browser.

Limitations to know

  • Banks usually use compound interest for deposits and reducing balance for loans.

Frequently asked questions

What is the difference between simple and compound interest?

Simple interest is on the principal only; compound interest is also earned on previous interest.

How do I enter months?

Choose “Months” — they are converted to years by dividing by 12.

Which day count is used?

365 days per year.

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