Blended Rate Mortgage Calculator
If you carry a first mortgage and a second loan or HELOC, your true cost is the blended rate. Find the weighted average across both.
How the blended rate mortgage calculator works
When you carry more than one loan against your home, no single rate describes what you actually pay. This calculator finds the blended rate, the single effective interest rate across a first mortgage combined with a second mortgage or HELOC. It weights each loan's rate by its share of the total balance, so the larger debt pulls the blend toward its rate.
The result is a true picture of your overall borrowing cost, useful when you are comparing a second loan against refinancing both debts into one new mortgage, or simply judging how a HELOC changes your effective rate.
Worked example: with first mortgage balance of $240,000, first mortgage rate of 6.00% and second loan / heloc balance of $45,000, the blended rate mortgage calculator shows blended interest rate of 6.395%.
- Combined balance
- $285,000
- Blended rate
- 6.395%
- Monthly interest
- $1,518.75
- Rate spread
- 6.00% / 8.50%
The formula
The blended rate is a balance-weighted average: multiply each loan's balance by its rate, sum those products across all loans, then divide by the combined balance of every loan. The result is the single rate that produces the same total interest as the separate loans.
- Rates are weighted by current balance, so the blend shifts over time as each loan amortizes at a different pace.
- A HELOC's rate is treated as fixed for the calculation, though variable lines actually move with the index.
- The blend reflects interest rates only and ignores differing fees, terms, and payment structures between loans.
- Interest-only or draw-period HELOC payments are not separated from fully amortizing first-mortgage payments.
- The figure is a snapshot; refinancing or paying down one loan changes the weighting and the blended result.
Results are estimates for educational purposes and are not financial advice. Confirm exact figures with your lender or a licensed advisor.
Questions about the blended rate mortgage calculator
Why would I want to know my blended rate at all?
It is the honest benchmark for comparison. When a lender offers to consolidate two loans into one, the new rate only helps if it beats your current blended rate, not just your higher second-loan rate.
The blend also reveals how much an expensive HELOC is quietly raising your overall cost of borrowing against the home.
Is a blended rate the same as my average rate?
Only if both loans had identical balances. A simple average treats each rate equally, but a blended rate weights them by how much you owe on each, which is what determines your real interest cost.
A small second loan at a high rate moves a simple average far more than it moves your true blended rate.
Does the blended rate change as I pay down my loans?
Yes, continuously. Because the blend depends on each loan's balance, paying down the higher-rate debt faster pulls your effective rate lower over time, while the slower-amortizing loan gains weight. That is why the calculator gives a present-moment figure. Recheck it after large principal payments or once a HELOC draw period ends.
Is the Blended Rate Mortgage Calculator free to use?
Yes. Every calculator on MortgageLoansCalculator is completely free, with no sign-up, login or paywall. Run as many scenarios as you like.
What is a blended mortgage rate?
When you hold two loans — say a first mortgage and a second or HELOC — the blended rate is the single effective rate across both, weighted by their balances.
It tells you the true cost of your combined debt and whether consolidating would help.
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