Rule of 72 and Compound Growth Explained
Understand the Rule of 72 as a quick growth estimate and why a compound-interest calculator gives a more precise scenario.
What the Rule of 72 estimates
Dividing 72 by an annual percentage return gives a rough estimate of the years required for money to double. For example, the rule is a mental shortcut, not a guarantee of investment performance.
Actual compounding is more precise
The true doubling period depends on the rate and compounding assumptions. A compound-interest calculation uses the mathematical growth formula and can incorporate recurring contributions.
Returns are not usually constant
Investments can rise and fall, and average returns do not arrive evenly each year. A smooth calculator projection is a scenario for planning, not a forecast of the path markets will take.
Fees and inflation matter
Investment fees reduce the amount that compounds, while inflation reduces future purchasing power. Long-term planning is stronger when you test more conservative net-return assumptions rather than only an optimistic headline return.
Use ranges instead of one forecast
Run low, middle and high return assumptions and compare the results. The spread between outcomes demonstrates how sensitive long-term projections are to small changes in assumed return.
Educational information only. This article is not individualized financial, investment, tax or legal advice and is not a lender, issuer or investment offer. Review current disclosures from the relevant provider before making a decision.