Simple Interest Calculator
Calculate Simple Interest, Principal, Rate, Time & ROI (Day / Month / Year)
This professional Simple Interest Calculator helps you instantly calculate interest, principal amount, rate of interest, time period and ROI. It supports daywise, monthwise and yearwise calculations and works completely on the client side.
Simple Interest Calculator – Calculate Interest, Principal, Rate, Time & ROI Online
A Simple Interest Calculator is a fast and reliable financial tool that helps you calculate interest, principal amount, rate of interest, time period, and ROI with accuracy. Unlike complex software or spreadsheets, an online calculator gives instant results and supports daywise, monthwise, and yearwise calculations.
Our Simple Interest Calculator is designed for students, investors, salaried individuals, business owners, and anyone who wants to understand basic interest calculations clearly. The tool works entirely on the client side using JavaScript, making it fast, secure, and easy to use on any device.
What is Simple Interest?
Simple Interest (SI) is a method of calculating interest where the interest is charged only on the original principal amount. The interest earned does not get added back to the principal for future calculations.
This makes simple interest easy to understand and commonly used for:
- Short-term loans
- Personal lending
- Basic savings calculations
- Educational purposes
Simple Interest Formula
Simple Interest = (Principal × Rate × Time) / 100
Where:
- Principal (P) = Original amount invested or borrowed
- Rate (R) = Annual rate of interest (%)
- Time (T) = Time period (in years)
How This Simple Interest Calculator Works
This calculator allows you to compute financial values in multiple ways. Instead of using only one formula, it supports different calculation modes:
- Calculate Simple Interest
- Calculate Principal Amount
- Calculate Rate of Interest
- Calculate Time Period
- Calculate ROI (Return on Investment)
Additionally, the calculator automatically converts time into years when you choose days or months, ensuring accurate results.
Calculation Modes Explained (With Examples)
1. Calculate Simple Interest
This is the most common use case. You provide the principal, rate, and time, and the calculator gives you the interest earned and total amount.
Example:- Principal: ₹50,000
- Rate: 8% per year
- Time: 2 years
Simple Interest = (50,000 × 8 × 2) / 100 = ₹8,000
Total Amount = ₹58,000
2. Calculate Principal Amount
If you already know the interest earned and want to find the original investment, this mode is useful.
Example:- Interest Earned: ₹6,000
- Rate: 10%
- Time: 2 years
Principal = (6,000 × 100) / (10 × 2) = ₹30,000
3. Calculate Rate of Interest
This option helps you find out the interest rate when the principal and interest are known.
Example:- Principal: ₹40,000
- Interest Earned: ₹4,000
- Time: 2 years
Rate = (4,000 × 100) / (40,000 × 2) = 5% per annum
4. Calculate Time Period
If you want to know how long it took to earn a certain amount of interest, this mode is helpful.
Example:- Principal: ₹25,000
- Interest Earned: ₹5,000
- Rate: 10%
Time = (5,000 × 100) / (25,000 × 10) = 2 years
5. ROI (Return on Investment) Calculator
ROI shows how profitable an investment is in percentage terms.
ROI Formula:ROI = (Net Profit / Investment) × 100Example:
- Investment Amount: ₹1,00,000
- Final Value: ₹1,20,000
ROI = (20,000 / 1,00,000) × 100 = 20%
Daywise, Monthwise, and Yearwise Calculation
One major advantage of this calculator is flexible time input. You can enter time in:
- Days (automatically converted to years using 365 days)
- Months (converted to years using 12 months)
- Years (direct calculation)
This makes the tool suitable for short-term loans, temporary investments, and quick interest estimates.
Why Use an Online Simple Interest Calculator?
- Instant and accurate results
- No manual calculations or errors
- Works on mobile, tablet, and desktop
- No login or personal data required
- Free and always available
Whether you are comparing loan options or planning a small investment, a simple interest calculator saves time and improves decision-making.
Frequently Asked Questions (FAQs)
What is the difference between Simple Interest and Compound Interest?
Simple interest is calculated only on the principal amount, while compound interest is calculated on the principal plus previously earned interest.
Is this calculator free to use?
Yes, the Simple Interest Calculator is completely free and works online without registration.
Can I calculate interest for days or months?
Yes, the calculator supports daywise, monthwise, and yearwise calculations automatically.
Is ROI the same as interest?
No. Interest is the cost or earnings on money, while ROI measures overall profitability in percentage terms.
Is this calculator accurate for financial planning?
The calculator provides accurate estimates for simple interest calculations, but for long-term investments, compound interest tools may be more suitable.
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