Entrovix AI

Simple Interest Calculator

Solves for whichever variable you are missing — including the rate you are actually being charged — with real day-count conventions and a compound comparison.

Runs in your browser — nothing is uploaded

What are you solving for?

Enter any three values and the fourth is worked out.

₹
% per year
years

Interest

₹30,000

Principal
₹1,00,000
Simple interest
₹30,000
Amount repayable
₹1,30,000
If it compounded instead₹3,100 more over the same term
₹1,33,100

Simple or compound is not a detail

On these terms compounding is worth ₹3,100 more — 10.33% on top of the interest. Worth checking which one your agreement actually says.
Why use it

Built to be genuinely useful

Solve for any variable

Know three of principal, rate, time and interest, and the fourth is worked out. Most calculators only do interest.

Real day-count bases

Actual/365, Actual/360 and 30/360. On a short-term loan the choice changes the interest by about 1.4%.

Compound comparison

See what the same money would have done compounded, so you know which one your agreement gives you.

Nothing is uploaded

Everything runs in your browser, so your figures never reach a server.

How it works

Three steps

  1. 1

    Pick the variable you want to find.

  2. 2

    Enter the three you know.

  3. 3

    For short-term loans, switch the term to exact days and choose the day-count basis.

The question people actually have

Working out the interest when you know the principal, rate and term is arithmetic anyone can do. The questions that send people to a calculator are the other three: I borrowed ₹2 lakh and repaid ₹2.4 lakh over eighteen months — what rate was that? I want ₹50,000 of interest at 8% — how long, or how much do I need to put in?

All three need the formula rearranged, which is where most people stop and most calculators do not help. Choosing the variable to solve for is the first control on this page rather than an afterthought.

The rate case is the one worth running on any informal loan. Interest quoted as a flat monthly amount on the original sum often works out at close to double the annual rate it appears to be, and seeing the figure stated as a percentage tends to change the conversation.

Why 360 or 365 days is not a technicality

Interest on a short-term loan is worked out per day, and the year has to be assigned a length to do that. Actual/365 is the Indian banking norm. Actual/360 is common in money markets and, because it makes each day worth more, produces about 1.39% more interest for the same nominal rate.

On ₹10 lakh at 12% for 90 days, Actual/365 gives ₹29,589 and Actual/360 gives ₹30,000. Over a single quarter that is ₹411. On a facility rolled repeatedly through the year it is not a rounding error, and the convention is a line in the agreement rather than something you are told.

30/360 treats every month as thirty days, which is the bond market convention and makes coupon periods equal. It is included because loan documents do sometimes specify it.

Flat rate versus reducing balance

Simple interest on the full original amount for the whole term is what lenders call a flat rate, and it is not the same as the rate on a reducing balance — the basis on which an EMI is calculated. A 10% flat rate on a five-year loan is roughly a 17.5% reducing-balance rate, because you are paying interest on money you have already repaid.

If you are comparing an instalment loan against a flat-rate quote, run the flat figure through here and the instalment through the EMI calculator. They are not comparable as quoted.

FAQ

Questions people ask

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