We just shipped 17 new finance calculators — full Groww parity, all client-side

We just shipped 17 new financial calculators in a single batch, bringing Stax's finance category to parity with Groww's calculator suite — the de facto standard reference for Indian retail investors. Same math, same currency formatting, same default values informed by FY 2025–26 government rates. The difference: every calculator runs entirely in your browser. Your salary, your loan amount, your portfolio cash flows — none of it touches a server.

Here's what we added, organized by what they actually solve.

Investment & mutual fund calculators

Lumpsum Calculator — Future value of a one-time investment. The simplest tool in the bunch, but the one that makes the compounding curve visceral: ₹1 lakh invested at 12% for 30 years grows to ~₹30 lakh, almost entirely from compounding.

SWP Calculator — Systematic Withdrawal Plan modeling. Critical for retirement planning. Shows whether your corpus survives the chosen tenure at the chosen monthly draw, or runs out early. The 4% safe withdrawal rate myth (sustainable in the US, often unsafe in India given inflation) becomes obvious once you run the numbers.

Mutual Fund Returns Calculator — Combo of SIP + lumpsum. Toggle between modes to compare the two approaches for the same total investment. For most salaried investors, SIP wins on discipline; for windfalls, lumpsum captures more compounding.

Step Up SIP Calculator — SIP with annual increases. The single most under-used calculator. ₹10k/month flat SIP for 25 years at 12% gives you ₹1.9 cr. Same SIP with a 10% annual top-up gives you ₹3.7 cr. The step-up percentage matters enormously over long horizons.

Stock Average Calculator — Weighted average buy price across multiple lots. Essential for anyone who DCAs into individual stocks or averages down. Optionally enter the current market price for unrealized P&L.

XIRR Calculator — The annualized return on irregular cash flows. This is the right metric for SIP returns, real estate investments, and angel deals — anything where money goes in at non-uniform dates. Newton-Raphson with bisection fallback so it converges even on adversarial inputs. If you've been computing your SIP return as (current_value − total_invested) / total_invested, you've been overstating it; XIRR is the honest number.

Government scheme calculators

EPF Calculator — Projects your Employee Provident Fund corpus at retirement. Accounts for the 12% + 3.67% combined contribution and annual salary hikes. For most salaried Indians, EPF will be the largest single retirement asset.

NSC Calculator — National Savings Certificate maturity. 5-year fixed tenure, 7.7% p.a. compounded annually, qualifies for Section 80C.

Sukanya Samriddhi Yojana — The girl-child savings scheme. ₹1.5 lakh/year for 15 years at 8.2% tax-free maturity at age 21 builds ~₹64 lakh — comfortably covers higher education at top private universities. The best small-savings instrument for parents of daughters under 10.

APY Calculator — Atal Pension Yojana monthly contribution lookup. Uses the official PFRDA contribution table, not estimates. Pick your target monthly pension and entry age, get the exact amount you need to deposit monthly until 60.

Post Office MIS Calculator — Monthly income from a POMIS deposit. Best paired with SCSS for senior-citizen monthly income planning.

SCSS Calculator — Senior Citizens Savings Scheme. Highest fixed-rate scheme available (8.2%), max ₹30 lakh per individual. Quarterly payouts.

Banking calculators

RD Calculator — Recurring Deposit maturity with quarterly compounding (the standard convention used by Indian banks and post offices).

Car Loan EMI Calculator — EMI calculator pre-set with typical car loan parameters (5-year tenure, 9% rate). The math is the same as the generic EMI calculator, but the defaults guide you toward sensible values.

Home Loan EMI Calculator — EMI calculator pre-set for home loans (20-year tenure, 8.75% rate). Plus the home loan affordability rule: keep EMI under 40% of take-home pay (lower if you have other EMIs).

Tax & trading calculators

TDS Calculator — Tax Deducted at Source for nine different payment types. Includes the no-PAN flat 20% rule under Section 206AA. Essential for freelancers, landlords, and business owners managing TDS deductions.

Margin Calculator — Estimates margin required for stock trades across equity intraday, delivery, futures, and options. Reflects post-SEBI peak-margin rules (lower retail leverage than pre-2021).

Why the privacy guarantee matters here

Most Groww-style calculator sites are run by brokers or fintechs whose primary motivation is to capture leads. Their calculators are the top of a funnel that ends with "open a demat account with us" or "buy this insurance product." That's a fair business model — but it changes the incentives. The numbers you put in (salary, loan amount, portfolio size) become marketing-qualified leads.

Stax doesn't have that funnel. We don't have a brokerage, an insurance product, or a fintech app to pitch. The calculator is the product. The numbers you put in stay in your browser. You can run a sensitive calculation (your actual home loan amount, your real CTC, your portfolio's XIRR including private holdings) without worrying that it becomes a CRM record or shows up in a retargeting ad three days later.

This was the original reason Stax exists, and it applies as much to finance tools as to JSON formatters.

What's next on the finance side

A few things on the roadmap:

Loan amortization schedule download — most Indian users want a year-wise principal-interest split they can save as PDF. Coming soon.
Inflation-adjusted retirement calculator — the existing retirement calculator shows nominal numbers. An inflation-adjusted version helps people understand the real purchasing power they're saving toward.
Tax regime optimizer — given your income and deductions, which regime (old vs new) saves more? The income tax calculator does this for static numbers; we'd like a slider that shows the breakeven across your full income range.
Pro tier integration — once Pro launches (Q3 2026), saved scenarios will let you persist multiple "what-if" calculations for the same calculator.

If there's a specific Indian finance calculator you want and we don't have it, email us — we keep a list and prioritize by what people actually ask for.

How to use these calculators for real financial planning

The calculators are most useful when you go beyond "what is the EMI on ₹50 lakh at 8.5%?" to more strategic planning questions. Here are three workflows worth walking through.

Workflow 1: Is your home loan affordable?

Most banks will approve a home loan where the EMI is up to 50–60% of your monthly income. But the right question isn't "will the bank approve it?" — it's "will I be comfortable with this EMI for the next 20 years?"

Start with the Take-Home Salary Calculator to find your actual monthly in-hand salary. Then use the Home Loan EMI Calculator to calculate the EMI for the loan amount you're considering. The EMI should not exceed 35–40% of your take-home pay — lower is better. Factor in other existing EMIs (car loan, personal loan) before finalising.

If the EMI is too high, check the Loan Prepayment Calculator to see what a moderate lump-sum prepayment of ₹1–2 lakh at year 3 does to total interest paid — often more impactful than you'd expect.

Workflow 2: Are you on track for retirement?

The retirement planning question in India is harder than most people realize because of the longevity risk (living to 90 on a corpus sized for 75) and inflation risk (7–8% Indian inflation erodes purchasing power faster than most Western assumptions).

Use the Retirement Calculator with conservative assumptions: 8% corpus growth (not 12%), 7% inflation, retirement age 60, life expectancy 90. The corpus number that comes out is sobering for most people. Then use the SIP Calculator to find the monthly SIP required to build that corpus given your current age. This is the exercise that makes people actually start investing.

Cross-check with the EPF Calculator to understand what your provident fund will contribute — for most salaried employees, this is 20–30% of the retirement corpus and is often forgotten in planning exercises.

Workflow 3: Old vs new tax regime

The 2023 budget made the new tax regime the default, but the optimal choice depends on your deductions. Someone with a home loan (Section 24 interest + Section 80C principal), HRA, and NPS employer contribution often saves more under the old regime. Someone without significant deductions typically pays less under the new.

Use the Income Tax Calculator in both modes with your actual CTC, deductions, and HRA figures. The difference can be ₹30,000–₹1,50,000 per year for salaries in the ₹10–20 lakh range — worth spending 10 minutes on.

The data you put in stays in your browser

It's worth reiterating: the salary number, the loan amount, the portfolio value, the real CTC — all of these go into browser memory and are computed locally. They are never sent to any server, never become part of any advertising profile, and are gone when you close the tab.

Most Indian finance calculator sites are operated by brokerages, banks, or insurance companies with a business reason to capture and retain that data. A realistic home loan calculation (₹80 lakh over 20 years from Mumbai) is a very high-value lead for a lender. Stax has none of that incentive — the calculator is the entire product.

What's next on the finance side

Loan amortization schedule download — most Indian users want a year-wise principal-interest split they can save as PDF. Coming soon.
Inflation-adjusted retirement calculator — showing real purchasing power, not just nominal numbers.
Tax regime optimizer — which regime saves more at your specific income and deduction level?
Pro tier integration — saved scenarios for multiple "what-if" calculations (Q3 2026).

If there's a specific Indian finance calculator you want and we don't have it, email us — we keep a list and prioritize by what people actually ask for.

My Take

The retirement calculator is the one tool in this batch most people run once and then set aside — when it should be revisited every year. The output shifts more than people expect: a 1% lower return assumption adds years to your accumulation timeline, and a 1% higher inflation assumption dramatically increases the corpus target. My suggestion is to run it with conservative inputs: 8% corpus growth (not 12%), 7% inflation, life expectancy 90, retirement age 60. The corpus number you see with those inputs is your real planning target — not the optimistic projection from 12% returns and 6% inflation. Most underfunded retirement plans I have seen used the optimistic scenario as their baseline. Use the conservative version as your floor instead.

The income tax calculator comparison is the other one worth spending genuine time on, not just clicking through. The regime decision for anyone with a home loan, HRA, and 80C deductions can swing ₹50,000–₹1.5 lakh annually. That is not a rounding error — it is a real monthly cash flow difference that compounds over 10 years of working life. Put in your actual CTC, your actual HRA, your actual loan interest figures — not round-number estimates — and let the calculator tell you which regime wins. The answer changes as income grows and deduction profiles shift, so it is worth redoing every April before you submit your employer declaration.

Grishma covers Indian markets and personal finance for Stax Tools. She tracks RBI policy, household budgets, and investment math for working Indian families.

— Built in 2026, in Ahmedabad.