How long to make your money 5 times at 11% return?

Based on these numbers, it takes about 15.42 years to reach that multiple.

11% p.a.

How is this calculated?

This uses the compound interest formula solved for time: years = ln(multiple) / (n × ln(1 + rate/n)), where n is the compounding frequency. At 12% annual compounding, for example, money roughly doubles in about 6 years, following the well-known "Rule of 72" approximation (72 ÷ rate).