How to use the simple interest calculator
- Enter the principal amount and the annual interest rate.
- Enter the time period and pick years, months or days. Months are divided by 12 and days by 365 to get years.
- Read the interest, the total amount and the interest per year and per month, then check the yearly table.
- Copy the summary if you need to paste it into a message or document.
Features
- Time in years, months or days
- Interest, total amount, and per-year and per-month interest
- Year-by-year table with cumulative interest
- Formula shown with your own numbers
- Sliders for quick what-if comparisons
The simple interest formula
SI = P × R × T ÷ 100, where P is the principal, R is the annual rate in percent and T is the time in years. The total amount is A = P + SI. Interest is charged only on the original principal, so it grows in a straight line: the same amount every year.
Worked example: 1,00,000 at 7.5% for 3 years gives SI = 1,00,000 × 7.5 × 3 ÷ 100 = 22,500, and a total of 1,22,500. For 18 months, T = 1.5, so the interest is 11,250.
Simple versus compound interest
With simple interest, last year's interest does not itself earn interest. Most bank savings accounts, fixed deposits and long-term loans use compound interest instead, where interest is added to the balance periodically. Simple interest is common for short-term personal loans, some vehicle loans, bonds and informal lending. If your product compounds, use the Compound Interest Calculator; the difference grows with time and rate.
Limits
This is an arithmetic tool, not financial advice. It assumes a fixed rate for the whole period and no fees, penalties or partial repayments. Lenders may count days differently (365 versus 360, or actual days in each month), which can change the result slightly. Check the exact figure with your lender or bank.