Rule of 72 - Doubling Calculator

Rule of 72 is one of finance's most elegant and practical tools: a simple mental-math formula that estimates how long your money takes to double at a given return rate. The formula: Doubling Time (years) = 72 ÷ Annual Return Rate. At 8% return, divide 72 by 8 to get 9 years—your investment doubles in 9 years. At 6% (FD rate), 72÷6 = 12 years. At 12% (equity returns), 72÷12 = 6 years. Remarkably accurate for rates between 1-15%, this rule helps savers intuitively grasp compounding power without complex calculations. The beauty: it makes wealth building concrete. 'I'll double my money in 9 years' is psychologically motivating versus abstract '8% return.' Many investors use Rule of 72 in retirement planning: starting at 25 with ₹1L at 8% = double to ₹2L in 9 years, ₹4L in 18 years, ₹8L in 27 years, ₹16L by age 52. This visualization of exponential growth motivates early and consistent investing. Understanding Rule of 72 transforms how you evaluate investments: is 1% higher return worth switching? Yes, because 8% vs 9% changes doubling time from 9 years to 8 years—one year of life given back. This calculator runs the exact math alongside Rule of 72 estimate, showing the formula's surprising accuracy across different rates and amounts.