Rule of 70 for retirement: How this simple formula helps estimate when savings may double

Planning for retirement requires careful consideration of how quickly your savings can grow over time. This estimate can give you an idea of the retirement corpus you might need and help you make prudent financial decisions.

The ‘Rule of 70’ is a simple formula that helps investors estimate how long it will take for their investments to double. It also assumes a constant annual rate of return to ensure clear calculations.

There are several alternatives to the ‘Rule of 70’; these are the ‘Rule of 72’ and the ‘Rule of 69’. These are yet another way that can facilitate constructive retirement planning.

Formula: Doubling time an investment will take = 70/ annual rate of return (%) on the investment

For example, if an investment earns about 7% annually, dividing 70 by 7 gives 10 years. This means that an investment can approximately double in 10 years, from ₹1 lakh to ₹2 lakh, if the annual return remains at 7%.

On similar lines, if an investment earns about 15% annually, dividing 70 by 15 gives 4.6 years. This means that an investment can double in about 4.66 years, from ₹1 lakh to ₹2 lakh, provided the return remains constant at 15% per annum.

It is also essential to keep in mind that this rule is an approximation; it can be used to gain insights and get an idea, but it is not a hard-and-fast rule.

How does ‘Rule of 70’ work?

The calculation can provide a quick way to understand the potential growth of retirement investments and determine how early one needs to start investing. It also highlights that delays in starting investments and low rates of return will eventually cost an individual dearly in later years. Let us look at some simple examples to understand the formula better.

The rule can help aspiring investors compare different return assumptions, asset classes and understand the impact of starting early.

What are limitations of ‘Rule of 70’?

The ‘Rule of 70’ works best when returns remain relatively predictable and stable, for example, in fixed deposits or savings bank accounts. They become less reliable for risk-based investments such as mutual funds, equities, gold and silver, and other similar asset classes, where returns tend to fluctuate with market conditions and geopolitical events. Along similar lines, periodic additions or withdrawals can cause the actual doubling to differ from the initial estimates.

Apart from these, it is also important to account for inflation, taxes, investment costs, and changing returns when calculating the required retirement corpus.

The ‘Rule of 70’ should be treated as an initial starting point for planning a constructive retirement. It should not be taken as a standalone strategy. A comprehensive retirement plan should consider income, expenses, expected inflation, investment returns and desired post-retirement lifestyle.

Disclaimer: The Rule of 70 is an approximate calculation and should not be treated as investment or retirement advice. Actual returns may vary due to market conditions, taxes, inflation and investment costs. Investors should seek professional financial guidance before making investment decisions.