For the rental yield based on the current property value, insert the property value into the form. For the rental yield based on the property purchase cost, you can enter the full amount into the box. On the other hand, you can also add additional charges, including stamp duty, mortgage fees and refurbishment costs, amidst others. Insert the monthly rent amount into the calculator. Insert a combined total value of your annual costs (if you have it ready) or add these individual costs separately to calculate the full amount. With all the information added, you can click to review your rental yield percentage.