The claim you have heard: a SIP means you buy more units when markets fall, so falls are good for you.
The claim is true. What is almost always left out is when it is true, and the condition is strict enough to change how you should think about the whole thing.
The mechanism
A SIP invests a fixed rupee amount, so the number of units it buys varies inversely with the price. Take ₹10,000 a month into a fund whose NAV moves around:
- NAV ₹100 → 100 units
- NAV ₹80 → 125 units
- NAV ₹50 → 200 units
- NAV ₹80 → 125 units
- NAV ₹100 → 100 units
You invested ₹50,000 and hold 650 units. Your average cost is ₹76.92.
Now note the arithmetic average of those NAVs: ₹82. You paid below the average price without predicting anything. That gap is rupee-cost averaging, and it is real — mathematically it is the harmonic mean sitting below the arithmetic mean, which is always true when prices vary.
In this example the NAV ended exactly where it started, at ₹100, and yet 650 units × ₹100 = ₹65,000 against ₹50,000 invested. A 30% gain from a market that went nowhere.
The condition nobody states
Read that example again. The fall recovered.
Rupee-cost averaging does not create return out of volatility. It creates return out of volatility followed by recovery. Every unit bought cheaply is only valuable because the price came back.
If the fund ends below your average cost, you have lost money — having accumulated more units on the way down simply means you own more of something worth less. A SIP into a permanently declining asset is a more efficient way to lose money, not a hedge.
This is why the fund you point a SIP at matters more than the SIP. Averaging is a purchasing discipline; it is not a substitute for owning something that recovers.
Why crashes are genuinely your friend — while accumulating
For someone still building a corpus, a long fall early is the best thing that can happen, and it feels like the worst.
The units bought at ₹50 in that table are the ones doing the heavy lifting at the end. An investor whose ten-year SIP contains a two-year bear market will usually finish ahead of one whose ten years rose smoothly, because a third of their units were bought at a discount.
The corollary is uncomfortable and worth stating plainly: if you are still accumulating, you should want lower prices. A rising market during your accumulation years is you paying more for the same eventual asset.
This reverses completely once you start withdrawing. Then falls force you to sell more units for the same rupee amount — the sequence risk covered in SWP.
The mistake that switches the mechanism off
Stopping a SIP because markets fell.
This is the single most common and most expensive SIP error. The cheap units are the entire benefit; pausing during a decline means you buy only the expensive ones and keep none of the advantage. It converts a mechanism designed to exploit volatility into one that is punished by it.
If a fall makes you want to stop, the issue is not the SIP — it is that your allocation is too aggressive for you, and the fix is at that level. See the psychology of a market crash.
Pitfalls to avoid
- Do not expect averaging to beat a lumpsum. If you already hold the money, staggering usually costs return, because markets rise more often than they fall. The honest comparison is in SIP vs lumpsum.
- Do not think it reduces risk. It reduces entry-price risk. Your exposure to the asset falling is unchanged.
- Do not run a SIP into a narrow thematic fund and call it prudent. Averaging into a concentrated bet does not diversify it.
- Do not obsess over the SIP date. The difference between the 1st and the 15th washes out within a couple of years.
Key takeaway
Rupee-cost averaging genuinely delivers a below-average purchase price, and a volatile decade that ends in recovery can beat a smooth one. But the benefit is conditional on recovery, and it is destroyed by the one thing investors instinctively do when it starts working: stopping. If you are accumulating, treat a crash as a discount on units you were going to buy anyway — and keep buying.
More in Module 2 — Mechanics and ways to invest
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The CAS: every fund you own, in one free statement
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Nomination: two minutes now, or a court process for your family later
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The twelve mistakes that cost first-time SIP investors the most
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