To know when will your SBI FD double up, you can use the rule of 72. Under this rule, the number â72â is divided by SBI FD interest rate applicable on your FD. The result is the number of years that it will take for your SBI FD to double up.
For example, if you are getting an interest rate of 7% on your fixed deposit in SBI, then as per the rule of 72, 72/7 = 10.2. Thus, it will take you a little more than 10 years to double your FD amount.