The question behind the question
“SIP or lumpsum?” is really two different questions wearing one hat. If the money already exists — a bonus, an inheritance, a maturing FD — the question is when to deploy it. If the money arrives monthly with your salary, there is no debate: SIP isn’t a strategy there, it is simply how salaries work. This page is for the first case.
What the arithmetic says
In a smooth-growth model, ₹6 lakh invested today at 12% for 10 years becomes about ₹19.8 lakh; the same ₹6 lakh drip-fed as ₹5,000 a month becomes about ₹11.5 lakh. The gap — over ₹8 lakh — is not magic, it is exposure: the lumpsum’s every rupee compounds for the full decade, while the SIP’s last instalment compounds for one month. The comparison above recomputes this with your numbers, and the conclusion never flips: in a rising model, earlier money wins. Historically, markets have risen more years than fallen, which is why studies across markets find immediate deployment beats staggered deployment roughly two times out of three.
What the arithmetic cannot say
The model’s smooth 12% hides the one thing that makes humans stagger money: sequence risk. Deploy ₹6 lakh the month before a 30% correction and years pass before break-even; the SIP in that same crash would have bought its way down and recovered faster — rupee-cost averaging earns its keep precisely when markets misbehave early. Staggering is thus best understood not as a return-maximiser but as regret insurance: it converts one big, possibly-terrible timing decision into many small, forgettable ones. The behavioural payoff is real — the investor who stays invested because they staggered beats the one who lumped in, panicked, and sold.
A sensible middle path
The practical Indian answer for a windfall: park it where it earns while it waits (liquid fund or a short FD, not a savings account), then deploy via STP over 6–12 months into your equity funds — longer staggering than a year mostly just dilutes returns. Size matters too: a bonus equal to two months’ SIP can go straight in; an inheritance equal to five years of savings deserves the staggered treatment, because its regret-capacity is larger than your experience with it. And whichever route you take, the projected result is only as good as the return assumption behind it.