Lesson 29 of 53 · The rule of 72 · 2 min read · Reviewed 29 Oct 2026
Divide 72 by the yearly return to get roughly how many years money takes to double. At 8% a year it takes about 9 years; at 12%, about 6. It works for prices too: at 6% inflation, prices double in about 12 years. The shortcut is close for returns between about 6% and 12%.
Divide 72 by the yearly return in percent. The answer is roughly the years it takes to double.
At 6% that is 12 years, at 9% eight years, at 12% six years.
The same works backwards: to double in 8 years you need about 9% a year.
Key idea: Run it on inflation too. At 6% a year, what costs ₹1 lakh today costs about ₹2 lakh in 12 years.
Try the short quiz on this page to check what stuck.
At 8% the exact answer is 9.01 years, so very close. It drifts at very high or very low rates.
Yes, using the return after tax, since tax is paid every year.
Use 115 instead of 72: at 10% money triples in about 11.5 years.
For learning only, not investment advice. Built in India by a team that tracks its own money on Reva.