Simple Interest Calculator

All tools

Calculate simple interest on a principal using the I = P·r·t formula. See interest earned, total amount and daily or monthly accrual instantly. Free.

$
%
Interest earned –
Total amount –
Principal –
Interest per month –
Interest per day –
Simple interest uses I = P × r × t with no compounding. Months are counted as 1/12 of a year and days as 1/365.

About Simple Interest Calculator

The simple interest calculator applies the classic formula I = P × r × t: principal times annual rate times time. Unlike compound interest, the interest never earns interest on itself, so the amount grows in a straight line.

Enter the principal, the annual rate and the time period in years, months or days — months count as 1/12 of a year and days as 1/365. The tool shows the interest earned, the total amount at the end, and how much interest accrues per month and per day.

Simple interest still governs many short-term loans, car title loans, some bonds and money owed between individuals, so it is worth checking before you sign or lend. This calculator is free and computes everything instantly in your browser.

How to use Simple Interest Calculator

  1. Enter the principal amount — the sum borrowed or deposited.
  2. Set the annual interest rate as a percentage.
  3. Enter the time period and choose its unit: years, months or days.
  4. Read the interest earned, the total amount, and the monthly and daily accrual.

Frequently asked questions

Simple interest is charged only on the original principal, so it grows linearly. Compound interest is charged on principal plus accumulated interest, so it grows faster over time. This tool computes the simple version only.

Enter the principal and rate, type 90 and select days as the unit. The calculator treats each day as 1/365 of a year, so t = 90/365 in the I = P·r·t formula.

Yes, enter the rate per year. If you only know a monthly rate, multiply it by 12 first — for example, 1% per month is 12% annually under simple interest.

Principal plus all interest earned over the period: A = P + I = P(1 + rt). It is what a borrower repays or a depositor holds at the end of the term.

Short-term personal and auto loans, some treasury and corporate bonds, late-payment penalties and informal lending often quote simple interest. Most savings accounts and mortgages compound instead.
Share this
Related Tools
Mortgage Calculator Estimate your monthly mortgage payment from the home price, down payment, term and interest rate, including property tax and home insurance. Free and instant. Free
Loan Calculator Calculate the monthly payment, total interest and total repayment on any loan from the amount, interest rate and term in years or months. Free and instant. Free
Auto Loan Calculator Work out your car loan monthly payment after down payment, trade-in and sales tax, plus the amount financed and total interest over the term. Free and instant. Free
Compound Interest Calculator See how your money grows with compound interest. Set the principal, rate, time, compounding frequency and an optional monthly contribution to get the future value. Free and instant. Free
Investment ROI Calculator Measure the return on an investment from its initial and final value. Get the ROI percentage, net profit, return multiple and annualized return over your holding period. Free and instant. Free
Retirement Calculator Project your retirement savings from your current age, savings, monthly contribution and expected return. See your balance at retirement, total contributions and growth. Free and instant. Free
Need help?
Found an issue with this tool? Let our team know.
Report an issue

Add this free tool to your own website — copy and paste the code below.