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Rule of 72

Rule of 72 Calculator

Back-of-napkin math for how long it takes your money to double. Divide 72 by your return rate.

Given Return → Find Time
Given Time → Find Rate
Years to Double Your Money
10.3
years
at 7.0% annual return
Doubling Time at Common Returns
Savings account (0.5%)144 yrs
High-yield savings (4%)18 yrs
Bonds (5%)14.4 yrs
S&P 500 avg (10%)7.2 yrs
Aggressive (12%)6 yrs
Doubling Time vs. Return Rate
$10,000 at 7.0% doubles to $20,000 in 10.3 years. It doubles again to $40,000 in another doubling period — that's the magic of compound growth.
Rule of 72 is an approximation. Exact formula: ln(2)/ln(1+r). Most accurate for rates 6–10%. Predictable Income

Rule of 72 Calculator

The Rule of 72 Calculator is the back-of-napkin classic every investor should have memorized, built into an interactive tool that works in both directions. Enter an expected return rate and the calculator instantly tells you how many years it takes your money to double, or flip the mode and enter a target doubling time to find the return rate you would need to hit it. A reference table shows doubling times at common yields, from savings accounts and bonds to the long-run average of the S&P 500, giving users an intuitive sense of how dramatically rate of return bends the timeline. The chart plots doubling time across the full range of return rates, visualizing the steep curve that makes small differences in yield matter enormously over decades. It is the calculator to pull up mid-conversation, the one that turns abstract percentages into something tangible: at this rate, your money doubles this many times in your working life, and that is the whole game.