Put a monthly SIP and a one-time lump sum next to each other over the same horizon and return assumption, and see how the invested amounts, returns, and final corpus differ.
The SIP side compounds each instalment from the month it is invested; the lump sum side compounds the whole amount from day one. Because the lump sum is invested for longer on average, it produces a higher corpus at the same rate — the comparison is most informative when you set the total invested amounts to be equal.
At a constant assumed rate, a lump sum always wins, because the money compounds for longer. Real markets are not constant: if the market falls after you invest, the SIP buys at lower prices and can end ahead. The constant-rate model here inherently favours the lump sum.
Historical studies generally favour investing immediately, since markets rise more often than they fall. Staggering over a few months reduces the regret if you happen to invest just before a fall. It is largely a question of which mistake you would find harder to live with.
This calculator is for information only and is not investment, tax, or financial advice. Figures are estimates based on the assumptions you enter and are not a guarantee of future returns. Consult a SEBI-registered adviser or a qualified tax professional before acting.