The ₹10,000 SIP That Could Become ₹33.7 Lakh: What Your SIP Calculator Shows — and What It Hides

Quick Answer: A SIP calculator projects your future corpus using the future value of a monthly annuity — compounding each instalment at an assumed annual return. At an assumed 12% over 10 years, ₹10,000 a month projects to about ₹23.2 lakh. Add a 10% annual step-up (raising your SIP every year) and the same calculator projects about ₹33.7 lakh. These are illustrative projections at an assumed rate, not guaranteed returns. Intro: Open any SIP calculator in India and type ₹10,000 a month, 10 years, 12% return. The screen flashes back ₹23.2 lakh. Then find the small "step-up" toggle, raise your SIP 10% every year, and the number jumps to ₹33.7 lakh — an extra ₹10.5 lakh, seemingly from nowhere. This article opens the black box: the exact formula, the year-by-year math of the step-up, what two years of real SIP data through the current market correction show, and the five things no calculator tells you — including a tax rule about your instalments that changes what you keep. Everything here is educational; nothing is a prediction about your money.

How a SIP Calculator Actually Works

Behind the slider and the growth chart, almost every Indian SIP calculator runs one formula — the future value of an annuity due: FV = P × [((1+i)^n − 1)/i] × (1+i), where P is your monthly amount, i is the monthly rate (annual rate ÷ 12), and n is the number of months. The × (1+i) at the end assumes each instalment is invested at the beginning of the month — the standard convention across Indian calculators (CNBC TV18's explainer and Franklin Templeton's official illustrations both use it). A few calculators use the end-of-month convention instead; on this example the difference is about ₹23,000 (₹23,23,391 vs ₹23,00,387) — enough to explain why two calculators occasionally disagree. The single most important input is the one you type freely: the expected annual return. Everything below uses 12% purely as an illustration — an assumption, not a promise or a forecast.

The Worked Example: ₹10,000 a Month for 10 Years

Using the standard formula at an assumed 12%: Monthly SIP: ₹10,000 Period: 120 months (10 years) Total invested: ₹12,00,000 Projected corpus: ₹23,23,391 Projected gains: ₹11,23,391 Read it carefully: the calculator says that if — a big if — your investments compound at a steady 12% a year, you roughly double your money in a decade. The "if" does all the heavy lifting, because real markets never deliver 12% in a straight line.

The Step-Up Trick: How ₹33.7 Lakh Appears

A step-up SIP raises your monthly amount by a fixed percentage — typically 10% — every year. Here is the year-by-year math at the same assumed 12%: Year 1: ₹10,000/month → year-end value ₹1,28,093 (invested ₹1,20,000) Year 2: ₹11,000/month → ₹2,85,241 (invested ₹2,52,000) Year 3: ₹12,100/month → ₹4,76,410 (invested ₹3,97,200) Year 4: ₹13,310/month → ₹7,07,323 (invested ₹5,56,920) Year 5: ₹14,641/month → ₹9,84,570 (invested ₹7,32,612) Year 6: ₹16,105/month → ₹13,15,734 (invested ₹9,25,873) Year 7: ₹17,716/month → ₹17,09,527 (invested ₹11,38,461) Year 8: ₹19,487/month → ₹21,75,956 (invested ₹13,72,307) Year 9: ₹21,436/month → ₹27,26,501 (invested ₹16,29,537) Year 10: ₹23,579/month → ₹33,74,326 (invested ₹19,12,491) The comparison, at the same assumed 12%: Flat ₹10,000/month: invested ₹12,00,000 → projected ₹23,23,391 Step-up ₹10,000 + 10%/year: invested ₹19,12,491 → projected ₹33,74,326 You invest about ₹7.1 lakh more and the projection rises by about ₹10.5 lakh — roughly 45% more corpus. Later, larger instalments still get years of compounding, and the step-up converts salary growth into investing growth before lifestyle inflation eats it. Most platforms let you set it once and forget it. Shorter horizon: ₹10,000 a month for 5 years at an assumed 12% projects to ₹8,24,864 on ₹6,00,000 invested. None of this recommends a step-up — it is a feature to understand. If your income is irregular, a fixed step-up can strain lean months; consider 5% or an annual manual review instead.

Crash-Test: What 2 Years of Real SIP Data Says

Projections are tidy; reality is the better teacher. An ET Bureau study (c. September 29, 2026) measured actual 2-year SIP returns by category: Small-cap: 14.25% Multi-asset allocation: 8.51% Mid-cap: 7.85% Multi-cap: 6.25% Large-and-mid-cap: 4.13% Large-cap and flexi-cap: 3.83% each Most categories beat their benchmarks (Nifty Smallcap 250 TRI: 9.78%). A separate ETWealth study (Sep 26, 2026) reported different figures — different universe and methodology — so note the study and date when quoting any ranking. The context matters. The week ending October 1 sealed an eighth straight weekly fall — the longest weekly losing streak in 25 years, with the Sensex touching a 52-week intraday low of 71,292.88 (weekend wraps: IANS, Economic Times, goodreturns). Foreign investors pulled ₹44,013 crore from Indian equities in September — yet monthly SIP inflows hit ₹32,297 crore in August 2026, up 37% from August 2024. Investors kept buying through the fall: more units per rupee when prices are low, the behaviour SIPs were designed to reward. History is not a promise — but it is why the 12% assumption is best read as "what a long, bumpy ride has sometimes averaged," not "what your statement will show."

Five Things Your SIP Calculator Hides

1. The assumed return is a guess, not a measurement. Calculators project; only XIRR measures. Your actual realised return — computed from your real instalment dates and amounts against real NAVs — will differ from whatever rate you typed. Judge a running SIP by its XIRR, not the calculator's headline number. 2. Tax comes off the gains, not the corpus. For equity mutual funds in FY 2026-27: gains on units held 12 months or less face 20% STCG; gains on units held longer face 12.5% LTCG on amounts above ₹1.25 lakh a year. Budget 2026 left these rates unchanged (Economic Times, February 2026). The calculator's headline number is always pre-tax. 3. Every instalment has its own 12-month clock. SIP units redeem first-in-first-out, and the 12-month holding period — for the LTCG/STCG line and the exit load — applies per instalment, not to the SIP as a whole. In a 14-month-old SIP, only the earliest instalments are long-term and load-free; recent ones can still attract 20% STCG plus exit load. 4. Exit loads are real and scheme-specific. The industry norm is around 1% if you redeem or switch within 365 days, and some schemes let the first 10% of units out load-free. But "typical" is not "universal" — always check your own scheme's SID (scheme information document) before assuming. 5. The 87A rebate does not rescue capital gains. The new-regime ₹60,000 rebate that makes salary income up to ₹12 lakh tax-free does not apply to capital gains taxed at special rates. And the calculator never adjusts for inflation or the fund's expense ratio — both quietly shrink the real, in-hand outcome.

When a Step-Up Fits — and When It Doesn't

A step-up suits investors whose income rises fairly predictably — salaried employees with annual appraisals, for instance. It suits them less when income is lumpy — freelancers, gig workers, business owners — because the rising commitment does not pause for a bad quarter. A middle path: start flat, add a manual step-up once a year after reviewing cash flow, or set the automatic step-up at 5% instead of 10%.

This article is for educational purposes only and is not financial advice. Please consult a SEBI-registered investment adviser for personalized guidance. Investments are subject to market risk.