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Free Simple Interest Calculator

Calculate simple interest, total amount, principal, rate or time — instantly. Covers Class 10 maths, bank exams (SSC, IBPS, RRB), personal loans, and gold loan checks with Indian rupee formatting.

₹
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—Interest (SI)
—Total Amount
—Principal
Principal vs Interest Breakdown—
Principal
Interest
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How to Use This Calculator
1

Choose what you want to find

Select a tab at the top — Find Interest (SI), Find Rate, Find Time, or Find Principal — depending on which value is missing in your problem.

2

Enter the known values

Fill in the three values you already know. Enter the principal in rupees, rate as a percentage per annum, and choose whether your time period is in years, months or days.

3

Click Calculate Now

The result appears instantly — you'll see the answer, the full formula with your values substituted in, and a visual breakdown of principal vs interest.

4

Use the Quick SI Checker in the sidebar

For a fast mental-math style check — enter principal, rate, and time in years and see the result update as you type. Great for exam practice.

💡For competitive exam problems, remember: if time is given in months, divide by 12; if in days, divide by 365 before applying the SI formula. This calculator does the conversion for you automatically.
🏦 Indian Lending Rates (2026)
RBI Repo Rate6.00%
SBI Personal Loan11–15%
SBI Gold Loan8.70%+
SBI Agri / KCC7.00%
HDFC Personal Loan10.85%+
ICICI Personal Loan10.85%+
Microfinance (NBFC)18–24%
Moneylender (max)~36%
Rates are indicative. Check official bank sites for current rates. Personal loans may use reducing balance, not simple interest.
⚡ Quick SI Checker
Principal (₹)
Rate (% p.a.)
Time (years)
Enter values to see quick result.
Result updates as you type. Use for fast exam-style checks.
📈 ₹1 Lakh @ 10% p.a. — SI Growth
₹10K
1 year SI
₹1,10,000 total
₹20K
2 year SI
₹1,20,000 total
₹30K
3 year SI
₹1,30,000 total
₹50K
5 year SI 🎯
₹1,50,000 total
₹100K
10 year SI
₹2,00,000 total
₹150K
15 year SI
₹2,50,000 total
With SI, interest stays flat every year — ₹10,000 regardless of year. Compare with compound interest using the CI Calculator.
📋 In This Page
  1. What is simple interest and how is it calculated
  2. The SI formula — all four rearrangements explained
  3. Where simple interest is used in India
  4. Indian bank and loan interest rates (2026)
  5. Simple interest vs compound interest — key differences
  6. 5 common mistakes in simple interest problems
  7. Frequently asked questions

What Is Simple Interest and How Is It Calculated?

Simple interest (SI) is the most basic method of calculating interest on a loan or investment. Unlike compound interest, where interest accumulates on previously earned interest, simple interest is always calculated on the original principal amount only. This means the interest amount stays constant every period — whether you are borrowing for one year or ten.

In India, simple interest is widely used in short-term borrowing, agricultural loans, government schemes, and school and competitive exam mathematics. Understanding it is not only a practical financial skill — it is essential for cracking SSC CGL, IBPS PO, RRB NTPC, SBI Clerk, and many other competitive exams where SI and CI problems appear in almost every quantitative aptitude section.

🏫
Class 10 & 12 Maths
Simple interest is a standard Class 8–10 topic in CBSE, ICSE and most state boards. It forms the base for understanding compound interest and banking concepts.
📝
Competitive Exams
SSC CGL, IBPS PO, RRB NTPC, SBI Clerk and UPSC prelims all include SI/CI problems in the quantitative aptitude section — typically 3–5 questions per paper.
🌾
Agricultural Loans
Kisan Credit Cards (KCC) and short-term agricultural loans from SBI and cooperative banks use simple interest at 7% p.a. — one of the lowest rates in India.
💎
Gold Loans
Gold loans in India — offered by banks and NBFCs like Muthoot and Manappuram — are quoted as simple interest rates, making them easy to compare and calculate.

The core concept in plain words

Imagine you lend ₹1,00,000 to a friend at 10% per year for 3 years, using simple interest. Every year, your friend owes you 10% of ₹1,00,000 = ₹10,000 in interest. At the end of 3 years, total interest = ₹30,000 and your friend pays back ₹1,30,000. The interest is the same every year — it does not grow because the base always remains ₹1,00,000. This is what makes simple interest simpler, more predictable, and easier to calculate than compound interest.

The SI Formula — All Four Rearrangements Explained

The simple interest formula has four variables: Principal (P), Rate (R), Time (T), and Simple Interest (SI). Knowing any three allows you to find the fourth. This is why competitive exam problems come in four types — each asking you to find a different missing variable.

Formula 1 — Finding Simple Interest

Standard SI Formula
SI = (P × R × T) / 100
Where: P = Principal (₹) · R = Rate per annum (%) · T = Time (years)

Formula 2 — Finding the Rate of Interest

Rearranged for Rate
R = (SI × 100) / (P × T)

Formula 3 — Finding the Time Period

Rearranged for Time
T = (SI × 100) / (P × R)

Formula 4 — Finding the Principal

Rearranged for Principal
P = (SI × 100) / (R × T)

Total Amount formula

Total Amount = Principal + Interest
A = P + SI  →  A = P + (P × R × T) / 100  →  A = P × (1 + RT/100)

Worked example — personal loan calculation

Example: ₹2,00,000 personal loan at 12% p.a. for 2.5 years — find total interest and amount payable
Step 1 — Identify the values: P = ₹2,00,000 · R = 12% p.a. · T = 2.5 years
Step 2 — Apply SI formula: SI = (2,00,000 × 12 × 2.5) / 100
Step 3 — Compute numerator: 2,00,000 × 12 = 24,00,000 · 24,00,000 × 2.5 = 60,00,000
Step 4 — Divide by 100: SI = 60,00,000 / 100 = ₹60,000
Step 5 — Total amount: A = ₹2,00,000 + ₹60,000 = ₹2,60,000
Total Interest = ₹60,000 · Total Amount Payable = ₹2,60,000 ✓
💡 Time unit shortcut for exams: If time is given in months, convert by dividing by 12. If in days, divide by 365. Example: 9 months = 9/12 = 0.75 years. 73 days = 73/365 = 0.2 years. Always convert to years before using the formula.

Where Simple Interest Is Used in India (2026)

While most long-term bank products in India now use compound interest or reducing balance calculations, simple interest still plays a key role in specific financial products, government schemes, and short-duration borrowing.

Kisan Credit Card (KCC) and Agricultural Loans

The Kisan Credit Card scheme, administered by NABARD and implemented by commercial banks and cooperative banks, offers short-term crop loans at 7% p.a. (with a 3% government interest subvention reducing it to 4% for prompt repayment). These are calculated as simple interest over the crop season — typically 6 to 12 months. For a ₹3,00,000 KCC loan at 7% for 6 months: SI = (3,00,000 × 7 × 0.5) / 100 = ₹10,500.

Gold Loans from Banks and NBFCs

Gold loans — one of the most popular short-term secured loan products in India — are typically quoted as simple interest rates. SBI's gold loan rate starts at around 8.70% p.a., while Muthoot Finance and Manappuram Finance (the two largest gold loan NBFCs) quote rates between 11% and 26% p.a. depending on the scheme and LTV ratio. Because gold loans are usually repaid within 6–12 months, the simple interest formula gives an accurate estimate of the interest payable.

Education Loan Interest During Moratorium

Under many government education loan schemes, interest during the study period (moratorium) is calculated as simple interest and either paid by the student or capitalised at the end. Under the Central Sector Interest Subsidy (CSIS) scheme, the government pays the simple interest during the moratorium period for eligible students.

Micro-Finance and NBFC Short-Term Loans

Microfinance institutions (MFIs) and small NBFCs often structure their loan repayments using a flat-rate simple interest calculation. While this makes the stated rate appear lower, the effective annual rate (EAR) is typically much higher because the principal reduces with each repayment. The RBI's fair practices code requires MFIs to disclose the effective interest rate — always check both the flat rate and the effective rate before borrowing.

⚠️ Important: Home loans, car loans, and most personal loans in India use reducing balance (diminishing principal) — not flat simple interest. With reducing balance, interest is calculated on the outstanding principal after each EMI payment, which means your effective interest cost is lower than the stated flat rate. Use the EMI Calculator for these loans, not simple interest.

Indian Bank & Loan Interest Rates — Simple Interest Reference (2026)

The following rates are commonly encountered in SI-based calculations for exams and practical financial planning. All rates are annual (p.a.) as published or stated by the institutions. Actual loan rates depend on your credit profile, loan amount, tenure, and current RBI policy rates.

Loan / Scheme TypeTypical SI Rate (p.a.)Lender / SourceRemarks
Kisan Credit Card (KCC)7.00% (4% after subvention)SBI, Cooperative BanksGovt. interest subvention for prompt repayment
Gold Loan — Bank8.70% – 11.00%SBI, PNB, CanaraShort-term, SI on outstanding
Gold Loan — NBFC11% – 26%Muthoot, ManappuramCheck effective rate carefully
Personal Loan — PSU Banks10.00% – 13.50%SBI, Bank of BarodaReducing balance in practice
Personal Loan — Private Banks10.85% – 18.00%HDFC, ICICI, AxisReducing balance; stated as p.a.
Microfinance Loans18% – 24%NBFC-MFIsFlat rate; effective rate much higher
Education Loan (CSIS scheme)8.00% – 9.00%SBI, Canara, UnionSI during moratorium; CI after
State Cooperative Bank Agri7.00% – 9.00%State Co-op BanksCrop season loans; SI basis

For exam problems, the most commonly used rates in India-specific SI questions are 5%, 6%, 7.5%, 8%, 10%, 12%, and 15% per annum. RBI repo rate, bank base rates, and scheme-specific rates also appear in banking exam general awareness sections.

SI in competitive exam problems — common question types

Question TypeWhat Is GivenWhat to FindFormula Used
Basic SIP, R, TSimple Interest (SI)SI = PRT/100
Total AmountP, R, TAmount (A)A = P + PRT/100
Find RateP, SI, TRate (R)R = SI×100/(P×T)
Find TimeP, SI, RTime (T)T = SI×100/(P×R)
Find PrincipalSI, R, TPrincipal (P)P = SI×100/(R×T)
SI–CI DifferenceP, R, T=2 or 3 yrsDifference (CI−SI)Diff = P(R/100)² for 2 yrs
Doubling TimeR givenYears to double (SI)T = 100/R years
Tripling TimeR givenYears to triple (SI)T = 200/R years

Simple Interest vs Compound Interest — Key Differences

Both simple and compound interest use the same inputs — principal, rate, and time — but they produce very different results over long periods. Understanding the difference is essential both for managing your finances and for solving exam problems accurately.

How they grow differently

With simple interest, the interest amount is the same every year — always calculated on the original principal. With compound interest, interest earned in each period is added to the principal, and the next period's interest is calculated on the new, larger balance. This "interest on interest" effect causes compound interest to grow exponentially over time.

FeatureSimple InterestCompound Interest
Interest BaseAlways original principalGrows each period (principal + accumulated interest)
Growth PatternLinear (straight line)Exponential (curve)
FormulaSI = PRT/100A = P(1 + R/100)^T
Total Interest (₹1L, 10%, 5 yrs)₹50,000₹61,051 (annually compounded)
Typical Use in IndiaGold loans, KCC, short-term borrowing, examsFDs, recurring deposits, home loans, SIPs
Easier To CalculateYes — mentally or on paperRequires exponent calculation
Better For LenderOver short periodsOver long periods
Better For BorrowerOver long periods (pays less)Over short periods
📌 Exam shortcut — SI vs CI difference formula: For 2 years, the difference between CI and SI = P × (R/100)². For 3 years: Difference = P × (R/100)² × (R/100 + 3). Memorise these — they appear in almost every banking and SSC exam.

For long-term wealth building — FDs, mutual funds, PPF — compound interest is far more powerful. For short-term borrowing where you want to minimise interest cost and keep calculations transparent, simple interest is more straightforward. Always verify which method a lender is using before signing any loan agreement.

🔄 Need Compound Interest? Try the CI Calculator

See exactly how much more you earn (or pay) with compounding vs simple interest — quarterly, monthly, or annual compounding, with Indian FD context.

Open CI Calculator →

5 Common Mistakes in Simple Interest Problems

Mistake 1 — Not converting time to years
✗ Wrong: P=₹60,000, R=10%, T=9 months → SI = (60,000 × 10 × 9) / 100 = ₹54,000
✓ Right: Convert months to years first → T = 9/12 = 0.75 years → SI = (60,000 × 10 × 0.75) / 100 = ₹4,500
The SI formula requires time in years because the rate is expressed as per annum (per year). If time is given in months, divide by 12. If in days, divide by 365 (or 366 for a leap year). Skipping this conversion is the single most common error in both Class 10 exams and competitive exam quantitative sections — and it inflates the answer by a factor of 12 or 365.
Mistake 2 — Confusing Amount (A) with Simple Interest (SI)
✗ Wrong: "Total amount payable is ₹18,000" when SI = ₹18,000 and P = ₹1,00,000
✓ Right: A = P + SI = ₹1,00,000 + ₹18,000 = ₹1,18,000 is the total amount payable
SI is only the interest earned or charged. The Amount (A) is the total you pay back or receive — it includes both the original principal and the interest. Exam questions often ask specifically for either "the interest" or "the amount" — read the question carefully. Answering with SI when asked for A, or vice versa, is a very common and avoidable mistake.
Mistake 3 — Applying compound interest formula to a simple interest problem
✗ Wrong: A = P × (1 + R/100)^T used for a simple interest problem
✓ Right: A = P + (P × R × T / 100) = P × (1 + RT/100) for SI
In SI, the multiplier is (1 + RT/100) — a linear function of time. In CI, it is (1 + R/100)^T — an exponential function. When a problem says "simple interest" or the context involves a gold loan, KCC, or short-term flat-rate loan, always use the SI formula. Mixing up the two formulas will give a wrong answer on every exam question of this type.
Mistake 4 — Using the wrong number of days in a year
✗ Wrong: For 73-day calculation — T = 73/360 years (banker's year)
✓ Right: In India, RBI and most banks use T = 73/365 = 0.2 years for simple interest on short-term loans
Some international banking conventions use a 360-day year ("banker's year") for simplicity. In India, the standard for most banking and exam purposes is a 365-day year. Check the problem statement — if it specifies 360 days, use that. If it doesn't, use 365. Competitive exams almost always use 365 unless stated otherwise.
Mistake 5 — Assuming home loans and car loans use simple interest
✗ Wrong: Calculating EMI for a ₹30 lakh home loan using the SI formula
✓ Right: Home loans use reducing balance (monthly compounding on outstanding principal) — use the EMI formula or an EMI calculator
Despite the common phrase "interest rate of 8.5% per annum," home loans and car loans in India do not use flat simple interest. They use the equated monthly instalment (EMI) method with interest charged on the reducing outstanding balance. The SI formula will dramatically underestimate the actual total interest paid on a 20-year home loan. For any EMI-based product, always use the EMI Calculator — not the simple interest formula.

Frequently Asked Questions

The simple interest formula is SI = (P × R × T) / 100, where P is the principal amount in rupees, R is the annual rate of interest in percent, and T is the time period in years. Total amount payable = P + SI. The formula can be rearranged to find any one variable — Rate R = (SI × 100) / (P × T), Time T = (SI × 100) / (P × R), and Principal P = (SI × 100) / (R × T).
Convert the time to years first, then apply the SI formula. For months: T = number of months ÷ 12. For days: T = number of days ÷ 365 (India standard). Example: 9 months = 9/12 = 0.75 years. 146 days = 146/365 = 0.4 years. The calculator above handles this conversion automatically when you select "Months" or "Days" as the time unit.
In simple interest, interest is always calculated on the original principal — so the interest amount stays the same every year. In compound interest, unpaid interest is added to the principal at each compounding period, meaning you pay interest on interest. For ₹1 lakh at 10% for 5 years: SI = ₹50,000 total interest, while annual compound interest = ₹61,051. The gap widens dramatically over longer periods.
Gold loans (from banks and NBFCs like Muthoot and Manappuram), Kisan Credit Card (KCC) agricultural loans, most short-term microfinance loans, and some cooperative bank loans use simple interest or flat-rate calculations. Home loans, car loans, and personal EMI loans use reducing balance method, which is different from flat simple interest. Always confirm with your lender which method applies to your loan agreement.
With simple interest, money doubles when SI = P, i.e., when PRT/100 = P. This simplifies to T = 100/R years. At 10% p.a., money doubles in 10 years. At 8% p.a., it takes 12.5 years. At 5%, it takes 20 years. Compare this to the Rule of 72 for compound interest — at 10% compound, money doubles in approximately 7.2 years, much faster than the 10 years needed for simple interest.
SI problems in SSC CGL, SSC CHSL, IBPS PO, RRB NTPC, and SBI Clerk exams fall into 8 types: finding SI, finding Amount, finding Rate, finding Time, finding Principal, the SI-CI difference shortcut (difference = P×(R/100)² for 2 years), doubling/tripling time, and combined SI+CI problems. Mastering all four rearrangements of the SI formula — and the SI-CI difference shortcut — covers almost all SI exam questions. Use this calculator to verify your manual working during practice.
Bank Fixed Deposits in India use compound interest, typically compounded quarterly. For cumulative FDs (where interest is not paid out), interest is added back to the principal every quarter, compounding over the tenure. Non-cumulative FDs pay out interest monthly or quarterly — this approximates simple interest in practice but the underlying calculation is still compounding. For FDs of less than 6 months or for certain special-purpose short-term deposits, some banks apply simple interest. Always check your FD confirmation letter for the exact method used.
As of June 2026, the RBI repo rate is 6.00% per annum. The repo rate is the rate at which the RBI lends money to commercial banks — it is the base rate that influences all lending and deposit rates in India. When the RBI cuts the repo rate, banks typically lower their lending rates (including gold loan and personal loan rates). When the repo rate rises, borrowing becomes more expensive. Most bank lending rates are now expressed as MCLR (Marginal Cost of Funds Based Lending Rate) or RLLR (Repo Linked Lending Rate), both tied to the repo rate.

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ToolLoom Team
📅 June 2026 · Written by the ToolLoom Team · Reviewed for accuracy June 2026
ToolLoom is a free tools platform built for Indian students, working professionals and exam aspirants. Our finance calculators follow RBI guidelines, CBSE syllabus standards, and Indian banking conventions. All interest rate data is verified against official bank websites and RBI publications at the time of writing.