Work out simple interest and the total amount from
your principal, annual rate and time — with a clear breakdown and a
quick comparison to compound interest.
🔒 Runs entirely in your browser — nothing is sent anywhere
Your loan or investment
The amount you borrow or invest, before any interest.
The interest rate charged per year.
Time period
Enter the duration in years, months, or both. We convert months to
a fraction of a year.
Whole years.
Extra months (0–11 typical).
How this works
Simple interest is the most straightforward way to price a loan or a
deposit — the interest is always a flat percentage of the original
amount.
1
Enter the principal
This is the amount you borrow or invest. Every rupee of interest is
calculated on this figure and only this figure.
2
Add the rate and time
Give the annual interest rate and how long the money is lent for,
in years and months. Months become a fraction of a year.
3
Read your result
We apply SI = P × R × T ÷ 100, add it back to the
principal for the total, and compare it to compound interest.
The formula in full
Simple interestSI = P × R × T ÷ 100
Total amountA = P + SI
Time (with months)T = years + months ÷ 12
Where P is the principal, R is the
annual rate in percent and T is the time in years.
Worked example
Borrow ₹1,00,000 at 10% for
2 years 6 months (T = 2.5). Then
SI = 1,00,000 × 10 × 2.5 ÷ 100 = ₹25,000,
and the total you repay is ₹1,25,000.
This is an estimate for planning. Real loans and deposits may differ
due to processing fees, day-count conventions, part-payments or a
rate that changes over time. Confirm the exact figures with your
lender or bank before committing.
🔒
Private by design. Every number stays on your device. Nothing you type is uploaded, stored or shared.
Frequently Asked Questions
What is the simple interest formula?▼
Simple interest is calculated as SI = P × R × T ÷ 100, where P is the principal (the amount you borrow or invest), R is the annual interest rate in percent, and T is the time in years. The total amount you repay or receive is simply P + SI.
How do I enter time in months?▼
Enter whole years and months separately — the calculator converts months to a fraction of a year using T = years + months ÷ 12. For example, 2 years 6 months becomes 2.5 years. You can leave either box blank if it doesn't apply.
How is simple interest different from compound interest?▼
Simple interest is charged only on the original principal, so it stays the same every year. Compound interest is charged on the principal plus the interest already added, so it grows faster over time. For the same inputs, compound interest is always equal to or greater than simple interest — this tool shows you both side by side.
Where is simple interest actually used?▼
Simple interest is common on short-term personal loans, some car and gold loans, many fixed-tenure deposits, and informal or friend-to-friend lending. Most long-term products like home loans, credit cards and mutual funds use compound interest instead.
Does the interest rate need to be per year?▼
Yes. This calculator treats the rate as an annual percentage. If you're quoted a monthly rate, multiply it by 12 first — for example, 1.5% per month is 18% per year. Then enter the total time using the years and months fields.
Is anything I type sent to a server?▼
No. Every calculation runs entirely in your browser using JavaScript. Your figures never leave your device and nothing is uploaded or stored.