Simple Interest Calculator
Calculate simple interest, total amount, and interest rate using Principal, Rate, and Time.
Simple Interest
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Total Amount
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What is Simple Interest Calculator?
A simple interest calculator computes the interest earned or paid on a principal amount at a fixed annual rate over a given time period, without any compounding. It is widely used for short-term loans, savings bonds, and introductory finance calculations. This calculator also lets you reverse-solve for rate or time when you know the other variables.
How to use
- 1 Select the 'Find Interest' tab to calculate interest from principal, rate, and time.
- 2 Switch to 'Find Rate' to determine the annual rate needed given principal, interest earned, and time.
- 3 Use 'Find Time' to see how long it takes to earn a target interest at a given principal and rate.
- 4 Fill in the three known values in the selected tab.
- 5 Results update instantly — interest amount and total repayable amount are shown side by side.
Formula
Example calculation
Borrowing ₹10,000 at 8% per annum for 3 years generates simple interest of ₹2,400 (10,000 × 8 × 3 / 100). The total repayable amount is ₹12,400. The same formula in reverse shows you need exactly 3 years to earn ₹2,400 in interest at that rate.
Frequently asked questions
When is simple interest used in practice?
Simple interest is used for short-term personal loans, certain government bonds, car loans with flat-rate structures, and some fixed deposits that pay interest periodically rather than compounding it.
Is simple interest better or worse than compound interest for borrowers?
Simple interest is generally better for borrowers because the interest is calculated only on the original principal. With compound interest, unpaid interest is added to the principal, leading to higher total debt over time.
How do I convert a simple interest rate to an effective annual rate?
For terms under one year, effective annual rate ≈ SI rate × (365 / term days). For comparison purposes, compound interest always produces a higher effective rate than the equivalent simple interest rate over the same period.
Can interest be negative?
In standard lending and saving scenarios, interest rates are positive. However, some central banks have implemented negative interest rate policies, which means depositors effectively pay to hold money at the bank.
What is the difference between flat rate and reducing balance interest?
Flat rate (simple interest) charges interest on the full original principal throughout the loan term. Reducing balance (used in EMIs) charges interest only on the outstanding principal, which decreases each month — making it cheaper overall.