Rule of 72 Calculator
The Rule of 72 estimates how long it takes money to double at a given interest rate. Enter your rate, starting amount, and projection years to see exact doubling time, number of doublings, and a growth curve chart.
How to use this tool
- Enter annual return rate, starting amount and projection years in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your years to double (rule of 72) and the full breakdown beneath it.
The Rule of 72 is a mental math shortcut: divide 72 by your annual return rate to estimate how many years it takes to double your money. At 6%, money doubles in 12 years. At 12%, in just 6.
Frequently asked questions
- How accurate is the Rule of 72?
- It's a good approximation for rates between 6% and 10%. For exact doubling time, use ln(2) / ln(1 + r) ≈ 0.693 / r.
- Does it work for debt too?
- Yes — at 18% APR your credit card debt doubles in roughly 4 years if you make no payments. The rule is a powerful reminder of compounding in reverse.