Simple Interest Calculator
This simple interest calculator uses the simple interest formula SI = P × R × T ÷ 100. Enter the principal, the annual rate of interest and the time period to find the simple interest (SI) and the total amount. Time can be entered in years, months or days — the calculator converts it for you and shows every step.
Step-by-step solution
- SI = (P × R × T) ÷ 100
- = (25,000 × 8 × 3) ÷ 100
- = ₹6,000
- Amount = P + SI = ₹25,000 + ₹6,000 = ₹31,000
How to use the simple interest calculator
- Enter the principal amount (P) in rupees.
- Enter the annual interest rate (R) in percent.
- Enter the time (T) and choose years, months or days. The interest and amount appear instantly.
Formulas
| Simple interest | SI = (P × R × T) ÷ 100T in years, R per annum. |
|---|---|
| Amount | A = P + SI |
| Principal | P = (SI × 100) ÷ (R × T) |
| Rate | R = (SI × 100) ÷ (P × T) |
| Time | T = (SI × 100) ÷ (P × R) |
Solved examples
Example 1: Find the SI on ₹25,000 at 8% per annum for 3 years.
- SI = 25,000 × 8 × 3 ÷ 100
Answer: SI ₹6,000, amount ₹31,000
Example 2: Find the SI on ₹12,000 at 9% per annum for 8 months.
- T = 8/12 years
- SI = 12,000 × 9 × 8/12 ÷ 100
Answer: ₹720
Example 3: In how many years will a sum double at 12.5% simple interest?
- SI = P, so P = P × 12.5 × T ÷ 100
- T = 100 ÷ 12.5
Answer: 8 years
Where simple interest is used
With simple interest, interest is charged only on the original principal, so it grows by the same amount every year. It is used for many short-term personal loans, some car loans, and in textbook problems. Most bank fixed deposits and savings accounts in India use compound interest instead.
A quick rule: at R% simple interest, money doubles in 100 ÷ R years. At 10%, that is 10 years; at 8%, 12.5 years.
Converting months and days into years
The rate is usually per annum, so time must be in years. Divide months by 12 and days by 365. For example, 146 days = 146/365 = 0.4 years. Some banks use 360 days for certain products, so check the terms if you need an exact match.
🎯 Asked in competitive exams
This topic regularly appears in the quantitative aptitude section of:
- SSC CGL & CHSL
- IBPS & SBI PO / Clerk
- RRB NTPC
- Campus placement aptitude tests
AI resume builder, ATS score check and interview practice.
Frequently asked questions
What is the formula for simple interest?
SI = P × R × T ÷ 100, where P is the principal, R is the annual rate of interest in percent and T is the time in years.
How do I calculate simple interest for months?
Convert months to years by dividing by 12, then use the formula. For 6 months, T = 0.5. Choose "months" in the calculator to do this automatically.
What are the simple interest and compound interest formulas?
Simple interest is calculated only on the principal: SI = P × R × T ÷ 100. Compound interest is calculated on the principal plus the interest already earned: with yearly compounding, CI = P × (1 + R/100)^T − P. That is why compound interest grows faster over time.
How do I find the principal from simple interest?
Rearrange the formula: P = (SI × 100) ÷ (R × T). If ₹1,800 is the SI at 6% for 3 years, P = 1,800 × 100 ÷ 18 = ₹10,000.
Is the answer rounded?
Values are shown rounded to 2 decimal places (paise). The calculation itself is done at full precision.
Keep learning
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