Simple Interest Calculator – Calculate Interest and Total Amount Online
By LegalDev India Tax Team
Simple interest is calculated only on the original principal for the entire loan or investment term, using SI = (Principal × Rate × Time) ÷ 100, with the total amount owed or maturing equal to Principal + SI. Unlike compound interest, the interest earned in year one never itself earns interest in year two — enter your principal, rate, and time below to get both figures instantly.
Use the calculator above to get your exact simple interest and total amount.
If you've ever tried comparing a gold loan quote against a personal loan quote and ended up with two numbers that don't seem to mean the same thing, the gap is often simple interest versus a reducing or compounding method, not a pricing trick. This calculator handles principal, rate, and time in years, months, or days, and shows you the interest and the total payable or maturing side by side — along with the one day-counting detail (Actual/365 versus 30/360) that most calculators skip and that can shift your answer by real rupees on a date-to-date loan.
What Is a Simple Interest Calculator?
A simple interest calculator takes your principal amount, annual interest rate, and time period, and returns the interest earned or owed using a fixed, non-compounding formula — interest calculated once on the original sum, never on sum plus previously earned interest. That single distinction is what separates it from a compound interest or EMI calculator, which recalculates the interest base at every period.
You'd reach for this tool over a general loan calculator when the product you're actually dealing with charges interest the simple way — common for gold loans, short personal loans between individuals, and bank fixed deposits with tenure under six months — since running those numbers through a compound-interest tool quietly overstates what you'll actually pay or earn.
How to Use the Simple Interest Calculator
Enter your principal amount in rupees, your annual interest rate as a percentage, and your time period, choosing years, months, or days from the unit selector depending on how your loan or deposit term is actually quoted. The calculator returns three figures: the simple interest for the full period, the total amount (principal plus interest), and, where useful, the equivalent monthly interest if you're trying to compare against an EMI-style product.
If you already know the interest amount and need to work backward — say, to check what rate a lender is actually charging — use the Find Rate, Find Time, or Find Principal tabs instead of the default Find Interest view; each rearranges the same formula to solve for the one variable you're missing.
Simple Interest Calculator Example
Two worked cases: one loan and one investment.
Loan example
You borrow ₹2,00,000 against gold jewellery at 12% per annum simple interest for 8 months. Converting 8 months to 8÷12 = 0.667 years, SI = (2,00,000 × 12 × 0.667) ÷ 100 = ₹16,000 (rounded). Total repayable at the end of 8 months = ₹2,16,000.
Investment example
You place ₹1,00,000 in a 5-month bank fixed deposit at 7% per annum. Banks pay simple interest, not compound interest, on deposits with original tenure under six months, so SI = (1,00,000 × 7 × (5÷12)) ÷ 100 = ₹2,917 (rounded). Maturity amount = ₹1,02,917.
How to Calculate Simple Interest for Months and Days
For months, convert T to years by dividing the number of months by 12 before applying the formula — 6 months becomes 0.5, 18 months becomes 1.5.
For days, divide the number of days by the day-count convention in use, and this is where two otherwise identical-looking calculators can disagree: the Actual/365 method (the convention the Reserve Bank of India uses for domestic term deposit interest) divides by 365 regardless of the specific days involved, while the 30/360 method treats every month as a flat 30 days for a 360-day year.
On a ₹5,00,000 loan at 9% for 157 actual days, Actual/365 gives SI = (5,00,000 × 9 × 157) ÷ (100 × 365) ≈ ₹19,356, while a 30/360 calculation over a similar nominal period lands on a slightly different figure — small on paper, but worth confirming with your lender when a loan is quoted date-to-date rather than in round months.
How to Calculate Rate, Time or Principal
Rearranging the same formula lets you solve for whichever variable you don't already have:
Rate: R = (100 × SI) ÷ (P × T) — use this to check what annual rate a lender is actually charging once you know the rupee interest, principal, and term.
Time: T = (100 × SI) ÷ (P × R) — useful for working out how long a given deposit needs to run to earn a target interest amount.
Principal: P = (100 × SI) ÷ (R × T) — useful for working backward from a known interest figure to the loan or deposit size that produced it.
Simple Interest vs Compound Interest
The difference is the base on which interest is calculated.
| | Simple Interest | Compound Interest |
|---|
| Calculation base | Always the original principal | Principal plus all interest accumulated so far |
| Growth pattern | Linear — the same rupee amount of interest every period | Exponential — the interest itself starts earning interest |
| Typical use in India | Gold loans, FDs under 6 months, some personal loans, informal lending | Recurring deposits, FDs of 6 months and above, savings accounts, most retail loans structured with reducing balance |
Over a single period both formulas agree; the gap only opens up as the term stretches past one compounding cycle, which is why a multi-year comparison always favours whichever side is earning compound interest and disadvantages whichever side is paying it.
Where Is Simple Interest Used?
Simple interest shows up in short-tenure and informal products.
Gold loans in India are commonly priced on simple interest for their typically short tenures, which is part of why they can look cheaper month-to-month than a reducing-balance personal loan at a similar headline rate.
Bank fixed deposits booked for less than six months also pay simple interest at maturity rather than compounding.
Informal lending between individuals — a loan to a relative, a chit fund settlement, a short vendor advance — is overwhelmingly calculated the simple way because it's easier for both sides to verify by hand.
Treasury bills and some short-term government instruments are priced on a similar non-compounding basis, though the exact day-count convention there follows its own market practice rather than the RBI's domestic deposit standard.
FAQs
SI = (Principal × Rate × Time) ÷ 100, with Time expressed in years.
Convert the months to years by dividing by 12, then apply the standard formula — 3 months becomes 0.25 years, 9 months becomes 0.75 years.
Divide the days by 365 (the Actual/365 convention most Indian banks use for deposits) or by 360 if your lender specifically uses the 30/360 convention, then apply the formula with that fraction as Time.
Simple interest is always calculated on the original principal alone; compound interest recalculates on principal plus all interest already earned, which is why compound interest grows faster the longer the term runs.
Only on deposits with an original tenure under six months — FDs of six months or longer typically compound at the frequency the bank specifies, usually quarterly.
Most gold loans in India are priced on simple interest, which is one reason their effective cost can look lower than a comparable personal loan over a short tenure.
Rate = (100 × Simple Interest) ÷ (Principal × Time), which backs out the annual rate once you know the other three figures.
Simple interest itself is always a positive figure for a positive rate and principal; what can mislead people is comparing it across unequal time periods without converting both to the same unit first.
It resembles it in shape but isn't the same calculation — A = P(1 + rt) is simple interest's total amount, growing in a straight line, while A = P(1 + r)^t is compound interest's total amount, growing exponentially; mixing the two up is the single most common error on this topic.
Using exact Actual/365 date-to-date calculation, a period spanning 29 February in a leap year still divides by 365 under the standard RBI convention rather than 366, which is a minor point but worth knowing if you're reconciling a lender's exact day-count statement against your own calculation.