Weighted Average Interest Rate: How to Calculate It (and Why It's Your Blended Rate)

If you carry more than one loan, the single most useful number you can know is your weighted average interest rate — the one rate that represents the true cost of all your debt combined. It is the number lenders use, the number federal student loan consolidation is built on, and the number you need before deciding whether to refinance.

A weighted average interest rate is the average of several rates, where each rate is weighted by its balance instead of counted equally. Larger loans pull the average toward their rate; smaller loans barely move it. In lending, this exact figure is called your blended rate — the two terms are interchangeable.

Calculate yours instantly:

Weighted Average vs Simple Average

A simple average treats every loan as equal. That is almost always wrong, because your loans are rarely the same size.

Say you have a $300,000 mortgage at 4% and a $10,000 credit card at 24%:

• Simple average: (4% + 24%) ÷ 2 = 14% — wildly misleading.
• Weighted average: the mortgage is 97% of your debt, so the true rate is 4.65%.

The simple average makes your debt look four times more expensive than it is. Only the weighted average tells the truth.

The Formula

Weighted Average Rate = Σ(Balance × Rate) / Σ(Balance)

Three steps:

1. Multiply each loan's balance by its rate.
2. Add those products together.
3. Divide by the total of all balances.

Worked Example

Weighted average = $12,225 ÷ $300,000 = 4.075%. A simple average of the three rates would have said 5.17% — over a point too high.

Where You'll Use It

• Student loans: federal Direct Consolidation is literally a weighted average of your existing loan rates.
• Mortgage + HELOC: find your true combined home-loan rate before a cash-out refinance.
• Debt consolidation: a consolidation offer only saves money if its rate beats your weighted average — check the math here.
• Corporate finance: the same weighting logic underlies WACC, the weighted average cost of capital.

A Note on Fees

The weighted average uses stated interest rates only. To compare a new loan offer that carries fees or points, you need its APR instead — APR bakes in those costs, while the weighted average describes the loans you already hold.

Frequently Asked Questions

What is a weighted average interest rate?

A weighted average interest rate is the combined rate across multiple loans, where each loan's rate is weighted by its outstanding balance rather than treated equally. It represents the true blended cost of all your debt. Larger balances influence the average more than smaller ones.

How do I calculate a weighted average interest rate?

Multiply each loan's balance by its interest rate, add all those products together, and divide by the total of all balances. For example, a $250,000 loan at 3.75% and a $50,000 loan at 6% gives (9,375 + 3,000) ÷ 300,000 = 4.13%.

Is a weighted average interest rate the same as a blended rate?

Yes. In lending, "weighted average interest rate" and "blended rate" describe the same calculation — a balance-weighted average of your loan rates. Federal student loan consolidation and mortgage-plus-HELOC analysis both rely on this figure.

Why use a weighted average instead of a simple average?

Because your loans are almost never the same size. A simple average treats a $300,000 mortgage and a $5,000 credit card as equally important, which grossly distorts your true cost. Weighting by balance ensures the rate reflects where your money actually is.

Does the weighted average include fees?

No. It uses stated interest rates and balances only. To account for origination fees, points, or closing costs on a new loan, use the APR, which is designed to include those charges.