What Is Simple Interest?
Simple interest is interest calculated only on the original principal, not on any interest already earned. It grows in a straight line, so over the same period it earns less than compound interest — which makes it common in some short-term loans but rare in long-term savings.
Why simple interest matters
Knowing the difference between simple and compound interest changes how you judge any loan or investment. The same rate can cost or earn very different amounts depending on which one applies.
For borrowers, simple interest on a short loan is predictable and easy to calculate. For savers, it is a reminder that you want compounding, not simple interest, working on your long-term money.
How simple interest works
With SI = P × R × T ÷ 100, the interest each year is a fixed percentage of the original principal and never changes, because past interest is not added back. So ₹1,00,000 at 8% simple interest earns ₹8,000 every year, whether it is year one or year ten. Compare that with compounding, where each year’s interest is calculated on a growing balance.
A real Indian example of simple interest
Put ₹1,00,000 at 8% for 10 years. With simple interest you earn ₹8,000 a year — ₹80,000 total, ending at ₹1,80,000. With compound interest at the same rate, the balance grows to about ₹2,15,000, because each year’s interest earns interest too. The gap widens the longer you stay invested, which is why long-term savers want compounding.
Benefits
Common mistakes
Best practices
Simple vs compound interest
| Simple interest | Compound interest | |
|---|---|---|
| Calculated on | Principal only | Principal + past interest |
| Growth | Straight line | Accelerating curve |
| Long term | Earns less | Earns much more |
| Formula | P × R × T ÷ 100 | P (1 + r/n)^(n·t) |
Frequently asked questions about simple interest
What is the simple interest formula?
SI = P × R × T ÷ 100, where P is the principal, R is the annual rate percent, and T is the time in years. The total amount repaid is the principal plus this interest.
How is simple interest different from compound interest?
Simple interest is calculated only on the original principal, so it stays constant each year. Compound interest is calculated on the principal plus accumulated interest, so it grows faster over time.
Where is simple interest used in India?
It appears in some short-term and vehicle loans and certain fixed-income calculations. Most savings products and long-term loans use compounding, so always confirm which method applies.
Is simple interest good or bad?
Neither on its own — it depends on your side. As a borrower on a short loan, simple interest is predictable and often cheaper than compounding; as a saver, you want compounding instead.
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How BudgetAnalyzer uses this
BudgetAnalyzer helps you free up money to save and invest, where compounding — not simple interest — does the heavy lifting. Track spending, lift your savings rate, and watch your invested balances grow in your net worth.
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