Rule of 72 calculator tells you how much time it takes for something to double given a certain level of constant growth rate. The term "doubling time" can be used interchangeably - our tool could as well be called "doubling time calculator", because that's exactly what it does. There's a nifty hack that lets you easily do it manually, see below to find out what is rule of 72. This is a special kind of compound interest where you want to work out how long it will take for something (for example your investment) to increase by 100%. It's a fairly narrow case, but it comes up quite often.
The rule states that in order to get the estimated doubling time, simply divide
72 by a percentage growth in a single period. For example, if something grows by
5% per minute, then it will double in roughly
72 / 5 = 14.4 minutes. The actual number is closer to 14.2067 - this should give you an idea of how much off you may be when you use the rule of a thumb method.
52 weeks, you know it needs to grow by