The SIP-vs-lumpsum debate is mostly answered by one question: do you already have the money? If you are investing from a monthly salary, a SIP isn't a strategy choice — it is simply how money arrives. The real debate only exists when a windfall lands: bonus, inheritance, property sale.
What the math says
In a market that rises over time, investing everything immediately beats spreading it out — more time in the market wins. Studies across markets (including backtests on the Sensex) find lumpsum outperforms a 12-month staggered entry roughly two times out of three.
What your behaviour says
The math assumes you stay invested when the market drops 20% the month after you invest. Most people don't. A staggered entry (an STP — systematic transfer plan — from a liquid fund into equity over 6–12 months) sacrifices some expected return to make panic-selling far less likely. A plan you can stick to beats an optimal plan you abandon.
A practical rule of thumb
- Monthly income → SIP. Automate it the day after salary credit.
- Windfall under ~6 months of income → invest it now. The stakes don't justify the ceremony.
- Large windfall → stagger over 6–12 months via STP, faster if the market corrects sharply while you're deploying.
- Money needed within 3 years → neither. Short-duration debt or FDs; equity is for long horizons.
Compare both side by side with real numbers in our SIP and Lumpsum calculators — same return assumptions, same horizon, your amounts.