GenzeeRule of 72 Calculator
Quickly estimate how many years it takes to double your money at a given annual return, using the classic Rule of 72 shortcut.
Years to double your money
~6.0 years
PKR 100,000 grows to PKR 200,000
What the Rule of 72 is
The Rule of 72 is a mental-math shortcut for estimating how long it takes an investment to double in value: divide 72 by the annual return percentage. At a 12% annual return, money doubles in roughly 72 ÷ 12 = 6 years — no calculator or compound interest formula required for a quick estimate.
Why 72 specifically
The number 72 is chosen because it divides evenly by many common small numbers (2, 3, 4, 6, 8, 9, 12), making the mental division easy, while still closely approximating the true logarithmic doubling-time formula across the range of return rates most people actually encounter (roughly 6-15%). Accuracy drifts slightly at very low or very high rates, which is why this calculator also shows the exact answer for comparison.
Why it's still useful in the calculator age
Even with instant access to precise calculators, the Rule of 72 remains valuable specifically because it's fast enough to do in your head — comparing two investment options' rough doubling times during a conversation, without reaching for a device, is exactly the situation it was designed for. It's a tool for quick intuition, not a replacement for precise planning.
Frequently asked questions
How accurate is the Rule of 72?
Very close for typical return rates between roughly 6% and 15% — usually within a few weeks to months of the exact compound-growth answer. Accuracy decreases somewhat at very low or very high rates, which this calculator shows directly for comparison.
Does the Rule of 72 work for inflation too?
Yes — the same shortcut works for estimating how long it takes inflation to halve the purchasing power of money, just applied to an inflation rate instead of a return rate.
Can I use this for debt instead of investments?
Yes — the same math shows how long an unpaid debt balance would take to double at a given interest rate if no payments were made, which is a sobering way to see high-interest debt's growth rate.