Two Interesting Mutual Fund investing “thumb rules”

Two Interesting Mutual Fund investing “thumb rules”

Read this blog to learn interesting thumb rules that can help you compare one time as well as SIP investments. To know more, Visit FinEdge Now!

Mutual Funds are fast growing in popularity among Indian savers, as can be evidenced by the fact that the total industry assets under management is touching nearly 40 lakh crores now. Here are two interesting thumb rules that you, as a mutual fund investor, may find useful when it comes to planning your goals using a SIP Return Calculator or a lump sum investment calculator.

The Rule of 72

The popular simple “Rule of 72” basically states that in order to arrive at the number of years it’ll take you to double your money at a given annual compound interest rate (say X%), all you need to do is divide 72 by X, and there you have your answer.

For instance – if your investment fetches you a compound annual interest rate of 10%, it’ll take you 72/10 = 7.2 years to double your investment. To be exact, a 10% CAGR investment will take you 7.3 years to double your investment – so it’s really remarkably accurate.

The reverse of the above applies as well – meaning that if your investment doubles in “X” years, the effective annualized return (CAGR) equals “72 divided by X” percent. For example – the recently re-launched Kisan Vikas Patra (KVP) doubles your money in 8 years and 4 months (8.33 years). Divide 72 by 8.33 and you’ve got the effective performance of the KVP – 8.67% per annum. Armed with this information, it becomes that much easier to compare the KVP to other investment avenues within similar risk categories.

It’s important to note that the Rule of 72 is a basically a rough estimation, and the accuracy diminishes as the return percentages or number of years becomes large. Also, the Rule of 72 applies to lumpsum (one time) investments only.

A number of investment products do not clearly specify an annualized return, but rather “disguise” their performance by specifying that “your money will double in X years”, making it difficult to make informed decisions about the product. For example, a “child insurance plan“ may promise to double your investment by the time your 6 year old child turns 18 years old (in 12 years’ time). Armed with the Rule of 72, you can now quickly calculate that the effective performance is 72/12 = 6% per annum.

But what about SIP investments?

As mentioned earlier, the Rule of 72 has practical applications for lump sum investments only. How then can you judge the performance of monthly savings options (such as recurring deposits or mutual fund SIP investment) in the same manner? For this, we present to you – “the rule of 128” SIP return calculator.

Let’s say that a specific recurring deposit specifies its performance in the following manner – “Save Rs. 10,000 per month for 15 years and receive double your money saved in the 16th year”. What is the CAGR? Easy – simply divide 128 by the time period (15 years) – and there you have the answer: 8.33%.

As with the “Rule of 72”, the “Rule of 128” has a reverse application as well. Let’s say you’d like to save Rs. 6 Lakhs over 10 years in monthly equal SIP investments (of Rs. 5000). What return do you need to generate in order to double the 6 Lakhs to 12 Lakhs? Simply divide 128 by the number of years (10 years) and there you have it – 12.8% CAGR!


In the above example, what if the number of “saving years” changes to 8 instead of 10? Firstly, the monthly SIP investment will change to Rs. 6250 (6 Lakhs divided by 96 months instead of 120 months). And applying the magic rule of 128, you’ll need a CAGR of 128/8 = 16% CAGR to double your 6 Lakhs to 12 Lakhs in 8 years. It works every time! Do keep in mind that just as with the Rule of 72, the SIP Return Calculator “Rule of 128” is a rough estimator, and the accuracy diminishes as the numbers get larger.

So, there you have it – two interesting thumb rules that can help you compare one time as well as SIP Investments. Happy Investing.

mutual fund investing rules

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