Simple Interest Calculator (SI = P × R × T ÷ 100)

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Quick answer

Enter a principal, an annual rate and a number of years to get the simple interest and the total amount from SI = P × R × T ÷ 100. Simple interest is flat: it is charged on the original principal only, never on interest already added. So ₹1,00,000 at 8% for 5 years earns exactly ₹40,000, and the total is ₹1,40,000. The calculation runs in your browser.

What the Simple Interest Calculator does

Enter a principal, an annual rate and a number of years, and the tool shows the simple interest and the total you would repay or receive. It recalculates as you type and works in rupees.

Simple interest is linear. The interest is the same every year because it is always a percentage of the original principal, not of a growing balance. That makes it easy to predict, and on a loan it costs less than compound interest at the same rate.

How it works

It uses the simple interest formula SI = P × R × T ÷ 100, where P is the principal, R the annual rate as a percentage and T the time in years.

The total is the principal plus that interest. Nothing compounds, so doubling the term doubles the interest and the growth never speeds up.

Methodology

Step 1. Take the principal P, the annual rate R (as a percentage) and the time T in years.
Step 2. Compute SI = P × R × T ÷ 100.
Step 3. Show the simple interest and the total amount, P + SI.
Step 4. Recalculate whenever an input changes.

Simple interest

SI = P × R × T ÷ 100
Total = P + SI
(P = principal, R = annual rate %, T = years)

Worked examples
₹1,00,000 at 8% for 5 years: 100000 × 8 × 5 ÷ 100 = ₹40,000 (total ₹1,40,000)
Each year adds the same ₹8,000, which is why it is called flat interest

The interest is always worked out on the original ₹1,00,000, so the yearly amount never changes. Compound interest on the same figures would earn more, because it also pays interest on the interest.

Assumptions

Interest is charged on the original principal only; nothing compounds.
One fixed annual rate for the whole term.
No part-payments, fees or tax.
Time is in years; for months, enter a fraction (6 months = 0.5).

Technical details

Inputs	Principal, annual rate %, years
Outputs	Simple interest, total amount
Growth	Linear (flat)
Currency	Rupees (₹)
Formula	SI = P × R × T ÷ 100
Where it runs	In your browser, as you type

Standards and references

SI = P × R × T ÷ 100: the standard simple interest formula, with interest on the principal only.
Linear growth: the same interest each period, so the total rises in a straight line, not a curve.
Common use: many car, personal and student loans, and some bonds, charge simple interest, which usually adds up to less total interest than compounding.

Accuracy and limits

It calculates flat interest only. Most savings accounts and fixed deposits compound, and for those this figure is too low; use the compound interest or FD calculator.

It assumes a constant rate and no part-payments. A loan you prepay builds up less interest than shown here.

Time is in years. For a period in months, enter the fraction: 9 months is 0.75.

The figure is gross, before tax or fees.

Real-world uses

Simple-interest loans

Estimate the interest on a car, personal or other flat-rate loan.

Quick flat sums

Get a fast, predictable interest figure for a short term.

Compare quotes

Put a flat-rate offer next to a compounding one to see the difference.

Teach the basics

Show how flat interest differs from compounding.

When it fits, and when it doesn't

Good for

Flat-interest loans and quotes
Quick, predictable interest sums
Comparing against a compound figure
Learning simple vs compound

Not the best choice for

Accounts that compound (savings, FD)
Recurring monthly investments
After-tax figures

For money that compounds, use the compound interest calculator. For a bank fixed deposit, use the FD calculator, which compounds quarterly. For monthly investing, use the SIP calculator.

Frequently asked questions

What is the simple interest formula?

SI = P × R × T ÷ 100, where P is the principal, R the annual rate as a percentage and T the time in years. The total amount is P + SI.

How is it different from compound interest?

Simple interest is charged only on the original principal, so it grows in a straight line. Compound interest is charged on the principal plus the interest already added, so it grows faster over time.

Where is simple interest used?

On many car, personal and student loans, and on some bonds. Over the same term it usually costs a borrower less than compound interest.

What does ₹1,00,000 at 8% for 5 years earn?

Exactly ₹40,000, from 100000 × 8 × 5 ÷ 100. The total is ₹1,40,000, and each year adds the same ₹8,000.

How do I enter a period in months?

As a fraction of a year: six months is 0.5, nine months is 0.75 and eighteen months is 1.5.

Does it compound?

No. The interest never earns interest of its own, and that is the difference between simple and compound interest.

Is simple interest cheaper on a loan?

At the same rate and term, yes. With no interest on interest, the total is lower than on a compounding loan.

Is tax deducted?

No. The figure is gross, before any tax or fees.

Is the rate fixed?

Yes. It assumes one annual rate for the whole term.

What's the difference between interest and total?

The interest is the amount added. The total is the principal plus that interest: what you would repay on a loan or hold at the end of a deposit.

Why does my savings account earn more than this shows?

Savings accounts and fixed deposits compound. They add interest to the balance and then pay interest on it, which this flat calculation leaves out.

What currency does it use?

Rupees. The formula works the same in any currency; only the symbol changes.

References

The calculator uses SI = P × R × T ÷ 100, so interest is charged only on the original principal. The total grows in a straight line and never earns interest on interest.

Compound Interest Calculator

See what a lump sum grows to with compound interest. Pick how often interest is added (yearly, quarterly, monthly or daily) and the rupee figures update as you type.