Blended Rate Calculator

Understanding the blended interest rate

A blended rate represents the combined, weighted average interest rate across multiple loans, debts, or tranches of financing. When you carry more than one debt with different principal balances and interest rates, simply averaging the rates produces a misleading number. The blended rate weights each interest rate by its proportion of the total outstanding balance, revealing the exact effective rate you are paying on your entire debt portfolio.

Blended rate calculations are essential when evaluating debt consolidation offers, second mortgages, home equity lines of credit (HELOCs), piggyback loans, or business credit lines. If you want to compute single-loan monthly installments, use our EMI calculator or test custom compounding intervals with our advanced loan calculator. To see how upfront lender charges and origination points influence borrowing costs, check our APR calculator.

When to calculate a blended interest rate

Calculating a blended rate is critical in several common real-world borrowing scenarios:

• First mortgage plus HELOC or second mortgage: Homeowners who locked in a low-rate first mortgage (such as 3.0% or 3.5%) often need cash for renovations. Instead of refinancing the entire loan at a higher prevailing market rate, they can keep their existing first mortgage and take a smaller second loan or HELOC. Calculating the blended rate reveals the true combined interest rate of both debts.
• Piggyback loans (80-10-10 or 80-15-5 financing): Homebuyers often split a purchase into an 80% primary mortgage and a 10% or 15% second mortgage to avoid paying private mortgage insurance (PMI). The blended rate indicates the actual net cost of financing the property.
• Debt consolidation: When combining credit cards, personal loans, and auto loans into a single consolidation loan, knowing your current blended rate gives you the exact target rate a new loan must beat to save you money.
• Corporate cost of debt: Businesses with multiple financing vehicles (senior credit lines, subordinated notes, equipment loans) calculate their blended interest rate to establish their weighted average cost of debt. To determine how tax deductibility lowers corporate financing costs, explore our after-tax cost of debt calculator.

Mathematical formula for blended rate

The blended rate is calculated by finding the total annual interest dollar amount generated across all loans and dividing that total by the combined principal balance:

Step by step, the calculation proceeds as follows:

1. Calculate the annual interest dollar cost for each individual loan: $\text{Interest}_i = \text{Balance}_i \times (\text{Rate}_i / 100)$.
2. Sum the total outstanding balance across all debts: $\text{Total Balance} = B_1 + B_2 + \dots + B_n$.
3. Sum the total annual interest dollar cost: $\text{Total Interest} = I_1 + I_2 + \dots + I_n$.
4. Divide total annual interest by total balance and multiply by 100 to obtain the blended annual percentage rate.

Worked example 1: First mortgage + Home equity loan

Suppose a homeowner has an existing first mortgage balance of $240,000 at a fixed rate of 3.50%. They need $60,000 for home improvements and take out a home equity loan at 8.50%.

• First Mortgage: $240,000 at 3.50% produces $8,400 in annual interest (represents 80% of total debt).
• Second Loan: $60,000 at 8.50% produces $5,100 in annual interest (represents 20% of total debt).
• Total Debt Balance: $240,000 + $60,000 = $300,000.
• Total Annual Interest: $8,400 + $5,100 = $13,500.
• Blended Interest Rate: $(\$13,500 / \$300,000) \times 100 = 4.50\%$.

In this case, the effective combined rate is 4.50%. If the homeowner were considering a cash-out refinance for the full $300,000 at today's market rate of 6.75%, refinancing would cost them significantly more each year ($20,250 in annual interest vs. $13,500 with the blended structure). For a full schedule of how payments pay down principal over time, see our amortization calculator, or test accelerated equity payoff with our biweekly mortgage calculator.

Worked example 2: Multi-debt consolidation portfolio

Consider an individual managing three distinct personal debts:

• Credit Card Debt: $10,000 balance at 21.0% interest ($2,100 annual interest).
• Auto Loan: $15,000 balance at 6.0% interest ($900 annual interest).
• Student Loan: $25,000 balance at 4.8% interest ($1,200 annual interest).

The total debt is $50,000, and the total annual interest is $4,200 ($2,100 + $900 + $1,200). The blended rate is $(\$4,200 / \$50,000) \times 100 = 8.40\%$.

A simple unweighted average of the three rates would give 10.60%, which overstates the true cost because the largest debt (the student loan) has the lowest interest rate. If the borrower is offered a consolidation loan at 9.50%, they should decline it, because 9.50% is higher than their current blended rate of 8.40%. However, transferring just the credit card balance to a 0% introductory card would dramatically lower their total cost. To evaluate that specific strategy, use our balance transfer calculator.

Blended rate vs. Simple average vs. Weighted term

Understanding how weighting impacts your financing decisions is crucial:

• Simple Average Rate: Adds all interest rates and divides by the number of loans, ignoring balance sizes. It should never be used for financial decisions.
• Blended Rate: Weights each rate by its dollar balance, giving a true snapshot of the interest rate paid per borrowed dollar.
• Weighted Average Term: Multiplies each loan balance by its remaining amortization period to determine the average duration of the debt portfolio.

Frequently asked questions