The latest articles on DEV Community by Subhransu Sekhar (@sekharsubhransu04). https://dev.to/sekharsubhransu04 https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F3962338%2F4c4dc9a7-56b7-466d-8bf4-6ebf8a516f3f.png https://dev.to/sekharsubhransu04 en Subhransu Sekhar Mon, 01 Jun 2026 08:51:42 +0000 https://dev.to/sekharsubhransu04/how-i-built-a-free-financial-calculator-suite-for-india-in-vanilla-js-no-frameworks-78d https://dev.to/sekharsubhransu04/how-i-built-a-free-financial-calculator-suite-for-india-in-vanilla-js-no-frameworks-78d <p>I got frustrated with existing Indian finance calculators. <br> They're slow, cluttered, require logins, and most don't <br> understand Indian-specific products like step-up SIPs, <br> floating rate EMI tracking, or the old vs new tax regime.</p> <p>So I spent a few weeks building one from scratch.</p> <h2> What it does </h2> <ul> <li>Home Loan EMI with full month-by-month amortisation table</li> <li>Prepayment tracking — add a lump sum on any month and see exact interest saved</li> <li>SIP, Step-up SIP and Lumpsum projections</li> <li>FD &amp; RD maturity calculator</li> <li>Old vs New Tax Regime side-by-side comparison</li> <li>Goal-based SIP planner with inflation adjustment</li> <li>SWP (Systematic Withdrawal Plan) calculator</li> <li>Multi-loan EMI comparison with Best Value highlighting</li> </ul> <h2> Tech used </h2> <ul> <li>Pure vanilla JS — no React, no Vue, no build tools</li> <li>Chart.js for all visualisations</li> <li>Single HTML file — entire app is one file</li> <li>Hosted free on Netlify</li> <li>Mobile responsive with CSS Grid and Flexbox</li> </ul> <h2> Interesting challenges </h2> <p><strong>Step-up SIP calculation</strong> was trickier than expected — <br> you can't use the standard SIP formula, you have to loop <br> month by month and increment the contribution every 12 months.</p> <p><strong>Prepayment tracking</strong> required rebuilding the entire <br> amortisation schedule dynamically on every input change, <br> recalculating every future month's opening balance.</p> <p><strong>Old vs New tax regime</strong> — the slab structures are <br> completely different so I wrote two separate tax functions <br> and run both on every calculation.</p> <h2> Live tool </h2> <p>👉 <a href="https://smartfoliotools.netlify.app" rel="noopener noreferrer">https://smartfoliotools.netlify.app</a></p> <p>Completely free, no login, works on mobile. <br> Would love feedback from the community — especially <br> if anything looks wrong on your device!</p> <h2> What's next </h2> <p>Planning to add:</p> <ul> <li>NPS calculator</li> <li>HRA exemption calculator </li> <li>Capital gains tax calculator</li> </ul> <p>Any other Indian finance tools you wish existed?</p> javascript opensource react software