Why I Built This
I wanted to build a small, practical project that focuses on real-world logic rather than UI polish or frameworks.
An EMI calculator felt like a good fit because it involves a clear formula, user input handling, and instant feedback.
The goal was to keep everything simple and readable while practicing core front-end fundamentals.
This is a learning-focused build log, not a product launch.
What the EMI Calculator Does
The calculator is intentionally minimal:
Takes loan amount, interest rate, and loan tenure as input
Calculates the monthly EMI instantly
Displays the result clearly
Works well on mobile devices
No charts, no advanced options, no extra configuration.
Tech Stack
I kept the stack basic on purpose:
HTML – structure and input fields
CSS – clean, responsive layout
JavaScript – EMI calculation logic and live updates
Using vanilla JavaScript helped me understand the math and state flow without abstractions.
EMI Calculation Logic
The Formula (Plain English)
EMI (Equated Monthly Installment) is calculated using this formula:
EMI = [P × R × (1 + R)^N] / [(1 + R)^N − 1]
Where:
P = Loan amount
R = Monthly interest rate (annual rate ÷ 12 ÷ 100)
N = Loan tenure in months
In this project:
Loan amount is entered as a number
Interest rate is entered annually and converted to a monthly rate
Tenure is entered in months
Core JavaScript Logic
Here’s the main calculation function:
function calculateEMI(principal, annualRate, months) {
const monthlyRate = annualRate / 12 / 100;
if (principal <= 0 || annualRate <= 0 || months <= 0) {
return null;
}
const emi =
(principal * monthlyRate * Math.pow(1 + monthlyRate, months)) /
(Math.pow(1 + monthlyRate, months) - 1);
return emi.toFixed(2);
}
To keep the UI responsive, the calculation runs whenever the user updates an input:
inputs.forEach(input => {
input.addEventListener("input", updateEMI);
});
function updateEMI() {
const principal = Number(amountInput.value);
const rate = Number(rateInput.value);
const months = Number(tenureInput.value);
const emi = calculateEMI(principal, rate, months);
result.textContent = emi ? Monthly EMI: $${emi} : "";
}
The focus here was clarity and correctness rather than optimization.
UI & UX Decisions
Design decisions were kept simple and practical:
Mobile-first layout
Clearly labeled input fields
Instant calculation instead of a submit button
Minimal styling to reduce cognitive load
The idea was to make the calculator understandable without instructions.
Edge Cases & Possible Improvements
Things handled or noted:
Empty inputs return no result
Zero or negative values are ignored
Assumes fixed interest rate only
Possible future improvements:
Total interest and total payment breakdown
Year/month toggle for tenure
Better validation and accessibility support
I intentionally kept these out to avoid scope creep.
Demo & Source Code
If you want to try it or explore the code:
Live demo: https://yuvronixstudio.github.io/emi-calculator/
Source code: https://github.com/YuvronixStudio/emi-calculator
Feedback
I’d really appreciate feedback from other developers, especially on:
Is the EMI formula implementation correct?
Any UI or UX improvements you’d suggest?
Better ways to structure the JavaScript logic?
This was built as a learning exercise, so constructive feedback is welcome.
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