By Ojasvi Malik, VMFS Research Desk · ARN 317605
Most Indians who start a SIP do so on gut feeling — ₹5,000 here, ₹10,000 there. They have a vague aspiration of "building wealth" but no hard number connecting today's monthly cheque to tomorrow's corpus. This post fixes that. You will leave with the exact formula, worked math, and ready-to-use tables. No black-box calculator required.
How SIP Compounding Actually Works
SIP is not a savings account. Every instalment you invest buys units at that day's NAV, and those units immediately begin compounding. The key mechanics:
Compounding frequency: Mutual funds compound daily on NAV, but for SIP projection math, the industry convention is monthly compounding. Monthly return r = Annual rate / 12.
Number of instalments: n = Years × 12
The correct SIP future value formula:
FV = P × [(1 + r)^n - 1] / r × (1 + r)
Where:
- P = monthly SIP amount (₹)
- r = monthly rate of return = Annual rate / 12
- n = total months = Years × 12
- (1 + r) outside the bracket = end-of-month compounding adjustment
Why the trailing (1 + r) matters: Bank SIP calculators often omit it, treating instalments as end-of-period payments. In reality, your bank debits the SIP at the start of each period. That one factor, over 25 years at 12%, inflates your corpus by roughly 1% — which on a ₹5 crore target is ₹5 lakhs real money.
Step-by-Step Formula Derivation
Let us derive the number for a ₹10,000/month SIP at 12% annual return over 20 years.
Step 1: Calculate monthly rate
r = 12% / 12 = 1% = 0.01
Step 2: Calculate n
n = 20 × 12 = 240 months
Step 3: Compute (1 + r)^n
(1.01)^240 = 10.8926
Step 4: Apply the formula
FV = 10,000 × [(10.8926 - 1) / 0.01] × (1.01)
= 10,000 × [9.8926 / 0.01] × 1.01
= 10,000 × 989.26 × 1.01
= 10,000 × 999.15
= ₹99,91,479 ≈ ₹99.9 Lakhs
At ₹10,000/month for 20 years at 12%, you land just shy of ₹1 crore. Precision matters.
Return Rate Assumptions: 10% vs 12% vs 15%
| Annual Return | ₹10,000 SIP × 20 Years | ₹10,000 SIP × 25 Years | |---|---|---| | 10% | ₹75.9 Lakhs | ₹1.33 Crore | | 12% | ₹99.9 Lakhs | ₹1.89 Crore | | 15% | ₹1.50 Crore | ₹3.29 Crore |
What to use in planning:
- 10%: Conservative. Large-cap or balanced advantage funds, within 5–7 years of goal.
- 12%: Realistic baseline for diversified equity portfolio with 15+ year horizon. Backed by Nifty 50 CAGR since inception (~13%).
- 15%: Aggressive. Mid/small-cap tilt. Valid only for 20+ year horizons where you can survive 40–50% drawdown cycles without panic-selling.
Never plan a retirement corpus at 15%. Use 15% for accumulation tracking, 10–11% for target-setting.
₹1 Crore SIP Table
Monthly SIP required to accumulate ₹1 Crore
| Horizon | At 10% Annual | At 12% Annual | |---|---|---| | 10 years | ₹48,800/month | ₹43,500/month | | 15 years | ₹24,400/month | ₹20,200/month | | 20 years | ₹13,200/month | ₹10,100/month | | 25 years | ₹7,500/month | ₹5,300/month |
The 10-year vs 25-year difference at 12%: ₹43,500 vs ₹5,300. Time is not an input — it is the product. Starting 5 years earlier cuts required SIP by 40–50%.
₹5 Crore SIP Table
| Horizon | At 10% Annual | At 12% Annual | |---|---|---| | 10 years | ₹2,44,000/month | ₹2,17,500/month | | 15 years | ₹1,22,000/month | ₹1,01,000/month | | 20 years | ₹66,000/month | ₹50,500/month | | 25 years | ₹37,500/month | ₹26,500/month |
If ₹50,000/month in SIP feels like a stretch today, note that step-up SIP can cut the starting amount by 30–40% while hitting the same terminal corpus.
Inflation Adjustment: Why ₹1 Crore in 2040 Is Not ₹1 Crore
India's CPI has averaged 5.5–6% over the last 15 years. At 6% inflation, ₹1 crore today is worth:
Real value in 15 years = ₹1,00,00,000 / (1.06)^15
= ₹1,00,00,000 / 2.397
= ₹41.7 Lakhs in today's money
So if your retirement target is ₹1 crore in today's purchasing power and you are 15 years away, you actually need to build ₹2.40 crore in nominal terms.
Practical rule: For every 12-year horizon, double your nominal target to account for 6% inflation.
Step-Up SIP Math: The Compounding Multiplier Nobody Uses
A step-up SIP increases your monthly contribution by a fixed percentage every year — typically 10%, mirroring salary growth.
Worked comparison — 20-year horizon at 12% annual:
Scenario A: Flat ₹10,000/month SIP → ₹99.9 Lakhs
Scenario B: Step-up SIP starting ₹10,000/month, 10% annual increase → approximately ₹2.0 Crore
Same starting amount. Same 20 years. Step-up 10% annually doubles the corpus.
Implication: If ₹50,500/month (flat, needed for ₹5Cr in 20 years at 12%) feels unaffordable today, start at ₹30,000/month with 10% step-up. Terminal corpus: ₹4.9–5.1 Crore. Far more achievable.
Worked Example: 28-Year-Old Wants ₹5 Crore by 55
Profile: Age 28, target retirement at 55. Horizon: 27 years. Goal: ₹5 crore nominal.
At 12% annual:
r = 0.01, n = 27 × 12 = 324 months
(1.01)^324 = 25.45
P = FV × r / [(1+r)^n - 1] / (1+r)
= 5,00,00,000 × 0.01 / [25.45 - 1] / 1.01
= ₹20,660/month
At 10% annual: ₹31,670/month — 53% more. That gap is entirely the return assumption.
Post-Tax Corpus: LTCG 12.5% Drag
Budget 2024 revised equity LTCG to 12.5% on gains above ₹1.25 lakh per financial year.
Tax drag on ₹5 crore corpus (28-year SIP example):
- Total invested: ₹20,660 × 324 = ₹66.9 lakh
- Gains: ₹5,00,00,000 - ₹66,90,000 = ₹4,33,10,000
- Exempt: ₹1,25,000
- Taxable gain: ₹4,31,85,000
- LTCG tax at 12.5%: ₹53,98,125 ≈ ₹54 Lakhs
- Post-tax corpus: ≈ ₹4.46 Crore
Smart mitigation: Systematic redemption over 3–4 years post-retirement harvests ₹1.25 lakh exempt gains per year. Tax planning is part of SIP planning, not an afterthought.
What Advisors Won't Tell You
Q: Why does my bank's SIP calculator show a different number than yours?
Bank calculators treat SIP as end-of-period payment and round monthly return to 2 decimal places. Over 25 years, that introduces a 0.3–0.8% error. At ₹5 crore scale, that's ₹15–40 lakhs of phantom precision.
Q: Should I use XIRR or CAGR to verify my SIP returns?
Always XIRR. CAGR is for lump-sum investments. SIP has irregular cash flows — each instalment has a different time in market. XIRR accounts for exact dates and amounts.
Q: What happens if I miss 2–3 SIP instalments during a job change?
Missing instalments does not break compounding on units already purchased — those keep growing. On a 25-year SIP, 3 missed months at year 10 costs roughly ₹60,000–₹90,000 in terminal corpus at 12% — painful but not catastrophic. The far worse mistake is stopping the SIP entirely during market falls.
Q: Why do step-up SIPs outperform flat SIPs so dramatically?
Later instalments in a step-up SIP are larger — but the real driver is that incremental capital added in middle years (years 8–18) has 7–15 years to compound — the sweet spot.
Q: At what point does SIP become insufficient and lump-sum becomes better?
When markets correct 25–40%, deploying lump-sum beats SIP for that specific entry point. Maintain SIP as baseline, deploy windfall bonuses as lump-sum during corrections. Never replace SIP with lump-sum speculation.
The Practical Execution Framework
- Fix your real target first. Nominal corpus = Real corpus × (1.06)^years.
- Choose return assumption conservatively. Plan at 11–12% for diversified equity.
- Start flat, step up. If required SIP exceeds 20% of take-home, start at 60–70% and step up 10% annually.
- Automate and ignore. SIP performance is inversely correlated with how often you check and react.
- Run tax math at accumulation stage. Systematic partial withdrawals post-goal to harvest ₹1.25 lakh exempt each year.
- Recompute every 3 years. Life goals shift. Markets over- or under-deliver. A 3-year recalibration catches drift before it becomes a 30-lakh gap.
Why Most Indians Underestimate the SIP Amount Required
Two systematic biases destroy corpus estimates before the SIP even starts.
Bias 1: Using pre-tax salary as the basis for SIP capacity.
If your CTC is ₹18 lakh, your monthly take-home (after professional tax, TDS, EPF) is approximately ₹1.1–1.2 lakh. Committing ₹20,000/month SIP is 17% of take-home — aggressive but achievable for a single person. Using CTC of ₹18L and calling ₹20K "only 1.3% of income" is fantasy accounting.
Bias 2: Ignoring goal inflation.
If your goal is "fund my child's MBA," the current cost of a top IIM programme is approximately ₹25–28 lakh. At 7% education inflation, in 15 years that MBA costs ₹70–80 lakh. The SIP calculator input should be ₹75 lakh — not ₹25 lakh. Underspecifying the target by 3x is the single most common corpus planning error.
Reverse Engineering: How Much to SIP for Any Corpus Target
The formula rearranges to solve for P:
P = FV × r / [(1 + r)^n − 1] / (1 + r)
Example: ₹2 Crore in 18 years at 12% annual return
r = 0.01
n = 18 × 12 = 216
(1.01)^216 = 8.4609
P = 2,00,00,000 × 0.01 / (8.4609 − 1) / 1.01
= 20,00,000 / (7.4609 × 1.01)
= 20,00,000 / 7.5355
= ₹26,543/month
A ₹26,543/month SIP for 18 years at 12% builds to ₹2 crore. Total invested = ₹26,543 × 216 = ₹57.3 lakh. Corpus = ₹2 crore. Return on investment: 249% absolute.
Step-Up SIP Tables: Reducing Starting SIP by 30–40%
Step-up SIP increases monthly SIP by a fixed % each year. The benefit: earlier instalments are smaller (easier when income is lower), later instalments are larger (matching salary growth).
₹1 Crore target at 12% CAGR — Flat vs Step-Up comparison:
| Horizon | Flat SIP Required | Step-Up SIP Start (10% p.a.) | Step-Up Saving | |---------|------------------|------------------------------|----------------| | 10 years | ₹43,500/month | ₹32,000/month start | 26% lower start | | 15 years | ₹20,200/month | ₹12,800/month start | 37% lower start | | 20 years | ₹10,100/month | ₹5,700/month start | 44% lower start |
Step-up SIP is not just behaviorally comfortable — it is mathematically equivalent to a higher flat SIP because increments in middle years compound for 7–12 more years before the goal date.
How to set up a Step-Up SIP: Most AMC apps (HDFC, ICICI Pru, SBI MF, Nippon) allow step-up configuration at registration. Input: initial SIP amount, step-up %, step-up frequency (annual is standard). The AMC automatically increases the NACH debit mandate each year. No manual action required.
ELSS Within Your SIP Plan: The Tax Multiplier
Every year you invest ₹1.5 lakh in ELSS (within 80C), you save:
- 30% bracket: ₹46,800/year
- 20% bracket: ₹31,200/year
- 10% bracket: ₹15,600/year
Over 20 years, that annual ₹46,800 saved and reinvested at 12% adds approximately ₹38 lakh to your terminal corpus. ELSS tax benefit is not a footnote — it is a corpus multiplier.
Constraint: ELSS maximum deductible is ₹1.5L/year. Cap your ELSS SIP at ₹12,500/month. Beyond that, route to non-ELSS equity funds.
The Sequence-of-Returns Problem for SIP Accumulation
SIP investors face a mirror-image of the sequence problem that retirees face. For accumulators, early-year bear markets are beneficial — you buy units cheap. Late-year bear markets (close to goal date) are harmful — you bought cheap earlier but the corpus final value drops.
Implication for goal-based SIP:
3–5 years before your goal date, start shifting accumulated corpus from equity SIP to debt/hybrid systematically. Do not wait until Year 15 of a 15-year SIP and redeem entirely in a bear month.
A practical glide path: in the last 3 years before goal, move 10–15% of equity corpus to short-duration debt each year. By goal date, equity exposure is 50–60% rather than 100%.
Common Calculation Errors: What Not to Do
Error 1: Using simple interest instead of compound interest.
₹10,000/month × 120 months × 12% annual = ₹1.44 crore? No — that is linear extrapolation, not compounding. Correct answer is ₹99.9 lakh (just below ₹1 crore). The naive multiplication overstates by 44%.
Error 2: Projecting CAGR returns as guaranteed.
12% is a planning assumption based on historical Nifty 50 performance. Actual outcomes vary. Plan with 10–11% for safety margin. If you get 13–14%, the surplus is a pleasant surprise.
Error 3: Not accounting for expense ratio drag.
1.5% expense ratio on a direct plan vs 0.1% index fund. On a ₹10,000 SIP over 20 years, this 1.4% annual drag compounds to approximately ₹15–20 lakh difference in terminal corpus. Always input the net-of-expense return into your SIP calculator, not the gross market return.
What Advisors Won't Tell You: Extended
Q: Should I stop SIP during a major market crash to protect capital?
This is the highest-cost mistake a long-term SIP investor makes. In every major correction — 2008, 2011, 2015–16, 2020, 2022 — SIP investors who paused missed buying units at the lowest NAVs of that cycle. Units bought during crashes are the ones that generate the highest returns during recovery. Stopping SIP during a crash is the equivalent of stopping grocery shopping when food goes on sale.
Q: Why does my SIP XIRR look worse than the fund's 5-year CAGR?
The fund's 5-year CAGR measures a lumpsum on a single start date. Your SIP distributes across 60 months — many at higher NAVs than the start date. XIRR accounts for this cash-flow timing. In a bull start followed by flat end, XIRR underperforms point-to-point CAGR. This is not a bug — it is the mathematical reality of averaged entry.
Q: At what corpus size should I switch from pure SIP to active allocation decisions?
When total equity MF corpus exceeds ₹50–75 lakh, decisions about how to deploy incremental capital — SIP top-up, new SIPs, lumpsum during corrections — are impactful enough to warrant quarterly review. Below ₹50 lakh, just run SIPs and ignore market noise.
This article is for educational purposes only and does not constitute investment advice. Mutual fund investments are subject to market risk. Past performance is not indicative of future results. Consult a SEBI-registered investment advisor before making investment decisions.
Registered Mutual Fund Distributor — AMFI ARN 317605 — By Ojasvi Malik, VMFS Research Desk Mutual fund investments are subject to market risks. Please read all scheme-related documents carefully before investing. Past performance is not indicative of future results.
Ojasvi Malik
VMFS Research Desk · ARN 317605
Building Vijay Malik Financial Services — research-first mutual fund discovery for retail investors who want institutional-grade analysis without the gatekeeping.
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