Finance · Loans
Simple Interest Calculator
Simple interest on the original principal only, with tenure in months. Live interest and total amount as you change the inputs.
Your simple interest plan
1,000 – 10 Crore
1% – 20%
1 – 120 months
Simple interest
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Growth over time
Principal vs interest by year
How this calculator works
Students, parents and borrowers use this page to sketch simple interest (SI) on the original principal: school maths problems, flat-rate style quotes and short study-period interest checks. Enter principal, annual rate (% p.a.) and tenure in months. You get simple interest and total amount (principal + interest).
This tool does not compute reducing-balance EMI, compound interest or FD maturity. Swap the page name to EMI calculator and these paragraphs stop fitting: the job here is SI on original principal with a months clock, not a monthly instalment schedule.
- Enter principal amount (₹1,000 – ₹10 Crore).
- Set annual interest rate (1% – 20% p.a.).
- Set tenure in months (1 – 120).
- Read simple interest, total amount and the growth chart as they update live.
Formula
SI = (P × R × T) / 100
Amount = P + SI
P= principal (₹)R= annual rate in percent (% p.a.)T= time in years = months ÷ 12
On this page tenure is entered in months. Convert before you apply the formula: 24 months → T = 2; 6 months → T = 0.5. Example: ₹1,00,000 · 8% p.a. · 24 months → SI = (1,00,000 × 8 × 2) / 100 = ₹16,000; amount = ₹1,16,000.
Assumptions: Interest on original principal only for the full tenure; no compounding; no monthly EMI amortisation; no processing fees, insurance or GST unless you fold those into principal yourself. Money figures follow page precision (2 decimal places).
Examples
More about this calculator
Who this calculator is for
Use it when you need SI on original principal: a school or college maths problem with P, R and T; a short flat or simple-interest style quote; a parent sketching study-period interest before repayment EMI; or anyone comparing SI with reducing-balance EMI so the two methods are not mixed up.
Do not use it for home, car or personal loan EMI schedules, compound growth or FD maturity. Those jobs live on other tools linked below.
What simple interest is
Simple interest is charged only on the original principal for the time you enter. Interest that already accrued does not itself earn more interest.
If you borrow ₹1,00,000 at 8% p.a. for 2 years under SI, interest is ₹16,000 for the whole period. The base stays ₹1,00,000; there is no year-2 interest on the first year’s ₹8,000.
Months to years on this page
The tenure field is in months (1–120). The formula still uses years: divide months by 12.
24 months = 2 years. 12 months = 1 year. 6 months = 0.5 year. Chip labels often show years for readability, but the slider and inputs stay in months. Mixing a year value into the months field will overstate interest.
Simple interest vs reducing-balance EMI
Most retail loans in India quote EMI on a reducing balance: each month interest is charged on what you still owe while principal falls as you pay. SI (and many “flat rate” brochure sketches) apply the rate to the original principal for the full tenure.
For the same headline % p.a., SI interest can look lower than total interest on a reducing-balance EMI schedule, or the quote methods can be hard to compare without converting. This page never returns an EMI. For instalments and schedules use the EMI calculator. Method context: EMI vs reducing balance and how EMI is calculated.
Simple interest vs compound interest
Compound interest adds earned interest into the base so later periods charge interest on a larger amount. SI does not.
Use this page for SI only. For compounding frequency and maturity-style growth, use the compound interest calculator. For bank FD sketches, use the FD calculator.
When borrowers see simple interest
You may meet SI framing in school maths, some short flat-rate style personal quotes and education-loan study or moratorium periods where interest is sketched on principal before full EMI starts. Product fine print still decides the real method.
A study-period SI sketch here is not the same as repayment-phase EMI. After study, model instalments on the education loan EMI calculator. Ask the lender whether study interest is serviced in cash or capitalised into principal.
What the default result means
Using the page defaults on first load (principal ₹1,00,000 · 8% p.a. · 24 months / 2 years), this calculator shows simple interest ₹16,000 and total amount ₹1,16,000.
SI is about 13.8% of the total amount (₹16,000 ÷ ₹1,16,000), or roughly ₹16 of interest for every ₹100 of principal. Amount is about 1.16× principal. On this default sketch, interest does not exceed the principal itself.
Decision angle: two years at 8% on ₹1 lakh under SI adds ₹16,000 before fees. That is a flat cost on original principal, not an EMI. If your quote is reducing-balance, switch tools. Change the sliders for your ticket; these figures are the default page-load example only.
Real-world examples
Chip presets match the scenarios below. Load a chip so the calculator lines up with the numbers. Situations cover a school SI problem, a short flat-rate style quote, a larger ticket and a half-year sketch.
Example 1: school SI problem (page defaults)
Situation: a student checks P, R and T for a two-year simple interest exercise that matches the page defaults.
Given: load 1L · 8% · 2y: principal ₹1,00,000 · rate 8% p.a. · 24 months.
Convert: T = 24 ÷ 12 = 2 years.
Result: simple interest ₹16,000 · total amount ₹1,16,000.
Takeaway: Interest is linear in time under SI. Doubling tenure at the same rate doubles SI when principal and rate stay fixed. See the insight block above for shares on these defaults.
Example 2: short flat-rate personal-style quote
Situation: a borrower checks a one-year flat or simple-interest style sketch on ₹5 lakh before comparing with EMI quotes.
Given: load 5L · 10% · 1y: principal ₹5,00,000 · rate 10% p.a. · 12 months.
Result: simple interest ₹50,000 · total amount ₹5,50,000.
Takeaway: One year at 10% on original principal adds ₹50,000 under SI. If the lender’s schedule is reducing-balance EMI, run the same ticket on the personal loan EMI calculator or the EMI hub and compare methods, not only the headline %.
Example 3: larger ticket over three years
Situation: a larger principal (for example a bigger education or personal sketch) held for 36 months under SI.
Given: load 10L · 12% · 3y: principal ₹10,00,000 · rate 12% p.a. · 36 months.
Result: simple interest ₹3,60,000 · total amount ₹13,60,000.
Takeaway: Larger tickets amplify rupee interest even when the % looks familiar. ₹3.6 lakh on ₹10 lakh over three years is a heavy SI bill before fees. Confirm whether the real product uses SI or EMI.
Example 4: half-year sketch
Situation: a six-month SI check for a short quote or a half-year maths problem.
Given: load 50k · 6% · 6m: principal ₹50,000 · rate 6% p.a. · 6 months.
Convert: T = 6 ÷ 12 = 0.5 year.
Result: simple interest ₹1,500 · total amount ₹51,500.
Takeaway: Half a year at 6% is half of one full year’s SI on the same principal. Enter 6 in months, not 0.5, or the interest will be wrong.
How tenure and rate change simple interest
Under SI, interest scales in a straight line with time and with rate when principal is fixed. The tables below use verified figures from this formula.
Tenure lever on ₹1,00,000 at 8% p.a. (only months change):
| Tenure | Simple interest | Total amount |
|---|---|---|
| 12 months (1 year) | ₹8,000 | ₹1,08,000 |
| 24 months (2 years) | ₹16,000 | ₹1,16,000 |
| 36 months (3 years) | ₹24,000 | ₹1,24,000 |
Each extra year at 8% on ₹1 lakh adds ₹8,000 of SI. Amount rises by the same step.
Rate lever on ₹1,00,000 · 24 months (only rate changes):
| Rate (% p.a.) | Simple interest | Total amount | SI delta vs 8% |
|---|---|---|---|
| 8% | ₹16,000 | ₹1,16,000 | baseline |
| 10% | ₹20,000 | ₹1,20,000 | +₹4,000 |
Takeaway: +2 percentage points on this two-year ₹1 lakh sketch adds ₹4,000 of SI. Stress a slightly higher rate before you treat a flat quote as settled.
Common mistakes
- Typing years into the months field (for example 2 instead of 24).
- Treating this SI result as reducing-balance EMI or monthly instalment.
- Comparing a flat SI brochure % with an EMI % without converting methods.
- Using this page for compound interest or FD maturity.
- Forgetting that SI ignores fees, insurance and GST on charges.
- Assuming every education loan uses SI for the full repayment phase.
Tips before you trust the number
Match the method on the quote: SI or flat-style on original principal stays here; reducing-balance EMI moves to an EMI tool. Keep tenure in months on this page and convert to years only inside the formula.
For study-period sketches, ask whether unpaid interest is capitalised before EMI starts. For investing rather than borrowing, prefer compound or FD tools instead of stretching this loan-side SI page.
Next steps after SI and amount
If the product is a reducing-balance loan, open the EMI calculator or the matching spoke such as personal loan EMI. For repayment-phase education tickets after study, use the education loan EMI calculator.
For compounding growth use the compound interest calculator. For deposit maturity sketches use the FD calculator. Flat vs reducing context: EMI vs reducing balance.
Important notes
Methodology: Simple interest SI = (P × R × T) / 100, where T = time_months ÷ 12 (years). Amount = P + SI. Precision on this page is 2 decimal places, matching the expression engine formulas.
Included: Principal, annual rate (% p.a.) and tenure in months that you enter.
Excluded by default: Compounding, reducing-balance EMI schedules, processing fees, insurance, GST on charges, penalties, floating resets, moratorium capitalisation rules and lender-specific day-count quirks unless you fold them into the inputs yourself.
Results are indicative estimates for education and comparison, not a loan offer, deposit quote or financial advice. Confirm any figure with the product’s sanction letter, term sheet or syllabus method.
Last reviewed: July 2026. Re-verify worked examples whenever defaults or rounding change.
FAQs
SI = (P × R × T) ÷ 100, where P is principal, R is annual rate in percent and T is time in years (months ÷ 12). Amount = P + SI. Precision is 2 decimal places.
The input is in months (1–120). Convert to years for the formula by dividing by 12. Example: 24 months → T = 2. Chip labels may show years for readability.
Usually not. Most retail loans use reducing-balance EMI on the outstanding principal. This page returns SI and amount only, never an EMI. Use the EMI calculator for instalments.
SI is charged only on the original principal for the tenure. Compound interest adds earned interest into the base so later periods grow on a larger amount. Use the compound interest calculator for compounding.
Commonly in school maths, some short flat-rate style quotes and education-loan study or moratorium sketches. Always read the product method. Repayment-phase EMI is a different job on the education loan EMI calculator.
No. Outputs are simple interest and total amount. There is no EMI, schedule or reducing-balance amortisation on this page.
No. Fixed deposits usually compound on a product schedule. Use the FD calculator for deposit sketches and the compound interest tool for general compounding.
On page defaults (₹1,00,000 · 8% · 24 months), SI is ₹16,000 and amount is ₹1,16,000. Interest is about 13.8% of the amount, or ₹16 per ₹100 of principal. Amount is about 1.16× principal. Interest does not exceed principal on this default.
SI applies the rate to original principal for the full tenure. Reducing-balance EMI charges interest on a falling balance. Same headline % can produce different total interest. Compare methods, not only the printed rate. See EMI vs reducing balance.
On ₹1,00,000 at 8% p.a., 12 months gives SI ₹8,000; 24 months ₹16,000; 36 months ₹24,000. Under SI, interest scales linearly with time when principal and rate stay fixed.
On ₹1,00,000 for 24 months, 8% gives SI ₹16,000 and 10% gives ₹20,000 (delta +₹4,000). Higher rate raises SI in a straight line under this formula.
No. Processing fees, insurance, GST on charges and penalties are excluded unless you raise principal yourself. Results are indicative, not a sanction or quote.
Yes, as a rough SI sketch on principal during study or moratorium when that is the stated method. It does not model capitalisation into EMI. After study, use the education loan EMI calculator for repayment-phase instalments.
If the loan is reducing-balance, switch to the EMI calculator or a product spoke such as personal loan EMI. For compounding or deposits, use compound interest or the FD calculator.