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SIP Calculator 2026: How SIPs Work

Understand SIP math, compounding, XIRR vs CAGR, rupee-cost averaging, and step-up SIPs. Includes realistic return expectations for Indian mutual funds.

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A Systematic Investment Plan (SIP) is a way to invest a fixed amount into a mutual fund at regular intervals — usually monthly. You’re not trying to time the market. You just buy units consistently, which smooths out price volatility over time and, more practically, removes the mental effort of deciding when to invest.

That simplicity is deceptive. The math behind it is genuinely powerful — but only if you understand what’s actually happening.

The SIP Math

For a monthly SIP of amount P over n months at an expected monthly return r:

$$FV = P \times \frac{(1+r)^n - 1}{r} \times (1+r)$$

Example: ₹10,000/month for 20 years at 12% annual return

  • P = ₹10,000
  • r = 12% ÷ 12 = 1% (0.01)
  • n = 240

Future value ≈ ₹99.91 lakh

You put in ₹10,000 × 240 = ₹24 lakh over 20 years. The remaining ₹75.91 lakh is returns on returns — compounding in action. You contributed less than a quarter of the final corpus.

The Compounding Curve Is Non-Linear

Most people visualize compounding as a straight line going up. It isn’t. The growth accelerates sharply in the later years — which is exactly why starting early matters more than starting big.

For the same ₹10,000/month SIP at 12%:

YearInvestedCorpusGains
5₹6L₹8.2L₹2.2L
10₹12L₹23.2L₹11.2L
15₹18L₹50.5L₹32.5L
20₹24L₹99.9L₹75.9L
25₹30L₹1.9Cr₹1.6Cr
30₹36L₹3.5Cr₹3.14Cr

Years 25–30 add ₹1.6 crore to your corpus even though you only invest an additional ₹6 lakh in that period. Starting 5 years earlier has the same effect as investing a significantly larger amount 5 years later — and that gap widens over time.

Rupee-Cost Averaging: Why SIPs Handle Volatility Well

When markets fall, your fixed monthly amount buys more units. When markets rise, it buys fewer units. Over time, your average purchase cost ends up lower than the market average — this is rupee-cost averaging.

That said, there’s a common misconception: that SIPs always beat lump-sum investing. Historical Nifty 50 data suggests lump-sum wins roughly 65% of the time for 10+ year horizons — simply because your money has more time in the market from day one. SIPs win during high-volatility periods and when you’re investing from monthly income rather than a lump sum.

The real value of a SIP isn’t necessarily mathematical outperformance. It’s behavioral: it removes the temptation to wait for the “right” time to invest.

Realistic Return Expectations

Most SIP calculators default to 12% or even 15%. These are optimistic projections. Based on historical data for Indian equity mutual funds:

  • Large-cap funds: 10–12% long-term CAGR
  • Mid-cap funds: 12–15% long-term CAGR (with considerably more volatility)
  • Small-cap funds: 14–18% long-term CAGR (significantly higher risk)
  • Index funds (Nifty 50): 11–12% long-term CAGR
  • Debt funds: 6–8% CAGR

For planning purposes, use 11–12%. Anything above that is a best-case assumption that depends on the decade, fund choice, and market conditions. Building a retirement plan around 15% is how people fall short.

CAGR vs XIRR — Why Your Fund’s “15% Return” Isn’t What You Earned

This is where a lot of SIP investors get confused when they check their portfolio.

CAGR (Compound Annual Growth Rate) measures the return on a single lump-sum investment made on day one. It’s what fund houses display on performance charts.

XIRR is the actual return you earned, accounting for multiple cash flows (your monthly investments) at different points in time. Your later installments had far less time in the market to compound.

A fund with a 15% CAGR over 10 years might deliver an XIRR of 12–13% on your SIP. That’s not deceptive — it’s arithmetic. The later installments simply had fewer years to work with. When comparing your portfolio return against a fund’s stated CAGR, always use XIRR for an accurate picture.

Step-Up SIPs: The Part Most Investors Skip

A step-up SIP increases your monthly contribution by a fixed percentage each year — typically 10%, roughly in line with expected salary growth. If your income is rising, your investments should too.

₹10,000/month SIP with 10% annual step-up, 20 years, 12% return:

  • Total invested: ₹68.73L (vs ₹24L with a flat SIP)
  • Final corpus: ₹1.83 Cr (vs ₹99.91L)

Nearly double the final corpus. And it happens automatically — you don’t have to remember to increase your SIP. Most fund platforms let you set this up once during enrollment.

Tax on SIP Gains

  • Equity funds (65%+ equity): LTCG after 1 year at 12.5% above ₹1.25L/year exemption. STCG at 20%.
  • Debt funds: Taxed as per your income tax slab (no LTCG benefit after the April 2023 rule change).
  • ELSS: 3-year lock-in per instalment, qualifies for Section 80C under the old tax regime.

Each SIP instalment has its own holding period. If you redeem units purchased 3 months ago and units purchased 3 years ago in the same transaction, the 3-year units get LTCG treatment and the 3-month units get STCG treatment. They’re not treated identically.

Common SIP Mistakes

  1. Stopping during market crashes. This is the single most expensive mistake SIP investors make. The entire benefit of rupee-cost averaging depends on buying during the dip. Stopping at the worst moment locks in losses and eliminates the recovery.
  2. Chasing last year’s top-performing fund. Fund performance rotates. A five-star fund this year may be average three years from now. Index funds or well-diversified equity funds tend to be more consistent for long-term SIPs.
  3. Too many funds. Owning 10 mutual funds doesn’t meaningfully diversify your risk — it mostly just creates overlap. Three to four funds is enough.
  4. Treating a SIP as an emergency fund. Equity SIPs are for 7+ year horizons. Emergency money belongs in a savings account or liquid fund — not in something that can be down 30% when you need it.

Use Our SIP Calculator

Our SIP Calculator lets you model step-up SIPs, compare flat vs step-up scenarios side by side, and see year-by-year corpus growth. Use the Compound Interest Calculator to compare SIP scenarios against lump-sum alternatives like FDs or PPF.