A SIP is a fixed monthly investment into a mutual fund. The amount is small enough to ignore and the horizon is long enough that the result is hard to picture, which is why the figures below are worth looking at. All of them come from our SIP calculator at an assumed 12% annual return, the long-run figure commonly used for diversified equity funds. It is an assumption, not a promise; the section at the end shows what changes if it is wrong.
₹5,000 a month, three horizons
| Horizon | Total invested | Value at 12% | Gains |
|---|---|---|---|
| 10 years | ₹6,00,000 | ₹11,61,695 | ₹5,61,695 |
| 15 years | ₹9,00,000 | ₹25,22,880 | ₹16,22,880 |
| 20 years | ₹12,00,000 | ₹49,95,740 | ₹37,95,740 |
Doubling the horizon from 10 to 20 years doubles what you put in and more than quadruples what you get out. The extra ten years of contributions are ₹6 lakh; the extra value is ₹38 lakh. The difference is compounding on the money that was already there.
The last five years do the most work
Between year 15 and year 20 the invested total rises by ₹3 lakh and the value rises by almost ₹25 lakh. That is not because the later contributions are special; it is because the ₹25 lakh already in the fund at year 15 grows at 12% for five more years while the new money is added on top. The pattern generalises: whichever horizon you pick, most of the final value arrives in the final third.
The practical implication is uncomfortable. Stopping a SIP at year 12 because the balance "looks small" abandons the years that would have produced most of the return.
Doubling the amount versus lengthening the time
₹10,000 a month for 15 years is ₹18 lakh invested and ₹50,45,760 at 12%. ₹5,000 a month for 20 years is ₹12 lakh invested and ₹49,95,740. The two end within ₹50,000 of each other. Five extra years bought the same result as doubling every contribution, for ₹6 lakh less in outlay. Starting early is cheaper than starting big.
The step-up SIP
Salaries rise, and a SIP that does not rise with them shrinks as a share of income. A step-up SIP increases the monthly amount by a fixed percentage every year. ₹5,000 a month stepped up 10% annually for 20 years invests ₹34,36,500 in total (the monthly amount reaches about ₹30,600 by year 20) and grows to ₹99,44,358. Same starting amount, same horizon, roughly double the ending value, funded by increments you would otherwise have absorbed into spending.
If the return is not 12%
The calculator lets you change the rate, and you should. At 10% the 20-year, ₹5,000 SIP ends around ₹38 lakh; at 14% around ₹66 lakh. The invested amount is the same ₹12 lakh in every case. Equity returns arrive unevenly, with flat years and sharp ones, and a SIP's monthly buying smooths the entry price but does not smooth the outcome. Use 12% as a planning figure and treat anything above it as a margin, not a plan.
What a SIP does not do
It does not remove risk; it spreads the purchase price over time. It does not guarantee the assumed rate. And it does not pay for a home loan: the EMI calculator shows that a ₹30 lakh loan at 8.5% costs ₹26,035 a month, which is five of these SIPs. Where the two meet is the tenure decision, since a shorter loan and a larger SIP compete for the same monthly surplus, and the honest comparison is loan interest saved against SIP return earned.