Calculate the weighted average of interest rates in Microsoft Excel to compute the most accurate average interest rate among a group of lenders who received different rates.

Divide the total weighted earnings by the weighted years to find the weighted-average five-year net income. Following the example, divide $1,810,000 by 15, which equals $120,667.

Weighted averages are used often in investing, especially in how we measure the performance of our portfolios. Here's the WACC formula.

The weighted average interest rate is used to determine your new interest rate if you decide to consolidate your federal student loans.