Equity markets are highly volatile. The shares prices vary considerably on day-to-day basis. In such a scenario, if you put a lump sum amount of money, you could either gain a lot or lose a lot. It would then become a kind of a lottery.
Instead, if you invested small amounts regularly, you will average out your total cost of acquisition. Thus, by doing Systematic Investment Planning (SIP) you will cut down the volatility risk and increase your chances of making money.
Debt markets, on the other hand, are relatively quite stable. If you put your money today or tomorrow or next month, it is not going to make much difference. As such, even if you were to put your lump sum in a debt fund, you are not likely to lose.
Therefore, the answer is simple:
• If it is a share or an equity fund, do SIP
• If it is a bank FD, NSC or debt MF, both SIP and lump sum are alright
Source : Moneycontrol.com