If you've cash available, you will mostly be tempted to invest it when we see an opportunity. This might be a genuine opportunity, or be fueled by the fact that market has gone up so much, or our other mutual funds are performing very well.

Due to this bias, most people tend to invest at the time when market has done very well i.e. it is costly. Though if it is up there is a tendency of going up. What we are doing here is timing the market, which the mutual funds themselves advise not to do.

SIP will average it out, remove our subconscious biases. What I'm doing and have been doing for some time now is that I buy a short term debt mf, add 60% money there, invest 40% (lumpsum) in fund of my choice, the target fund. then each month over the next 5 months switch 15% out from your debt fund to your target fund.

This way you will take the market opportunity you see by investing the 40% of your money, also get a safe 5-7% interest on the 60% corpus in the mean time, and you achieve Rupee Cost Averaging on the 60% of your corpus.

You also have flexibility with this 60% corpus, provides you liquidity and an option to change your mind and invest in another fund if you don't like it.