If you're just getting into investing and fast maths isn't your strong point, you can quickly see how long it will take to triple your investment with the rule of 115.
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When determining how long it will take to double your investment quickly, you would use the rule of 72. All you need to do is divide the number 72 by your projected growth rate. If you want to know how long it would take to triple it however, Andy Kiersz at Business Insider suggests you use 115 instead. For example, if you're getting a return of 5 per cent, you would divide 115 by 5, telling you that your investment will triple in 23 years. Both the rule of 72 and the rule of 115 work because they're just manipulating the formula for calculating compound interest.
Neither rule will provide precise results, but it will give you an idea of how long you're looking at. It's also important to consider inflation and other factors, but this is more a quick trick and not a guaranteed accurate number.
7 Maths Tricks That will Make Your Life Easier [Business Insider]