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.
A worked example
Running this tool on current national benchmarks (Federal Reserve / Freddie Mac via FRED (St. Louis Fed)) — swap in your own numbers to see how the result moves.
- First mortgage balance
- $240,000
- First mortgage rate
- 6%
- Second loan / HELOC balance
- $45,000
- Second loan rate
- 8.50%
- Years remaining
- 25
on $285,000 of combined mortgage debt
- Combined balance$285,000
- Blended rate6.395%
- Monthly interest$1,518.75
The math behind it
When you carry two loans against your home — a first mortgage and a second loan or HELOC — the calculator computes the balance-weighted average of their rates. It multiplies each balance by its rate, adds the two, and divides by the combined balance. That blended rate is your true cost of carrying both debts, and the calculator also shows the monthly interest and amortizes the combined balance at the blend.
Assumptions & limits
- The blended rate is a simple balance-weighted average, which is exact for interest cost at a point in time. It does not account for the two loans having different terms or payoff schedules.
- Both balances are assumed to run over the same remaining term when amortized at the blend.
- A HELOC's rate is usually variable; the calculator treats the rate you enter as fixed for the projection.
- Payments shown are principal and interest on the combined debt — taxes, insurance, and fees are excluded.
Source: Freddie Mac PMMS via FRED. Annual averages; latest weekly reading shown.
Common questions
Why does the blended rate matter?
It is the single number that represents what all your home-secured debt actually costs. When you weigh a cash-out refinance that would consolidate both loans, the new rate only helps if it beats this blend — comparing it to just your first mortgage rate can be misleading.
Is the blended rate a simple average of the two rates?
No — it is weighted by balance, not a plain average. A large first mortgage at a low rate and a small second at a high rate produce a blend close to the first mortgage's rate, because most of the debt sits there. The bigger balance pulls the blend toward its own rate.
When should I refinance to escape the blend?
Only when you can find a single loan priced below your blended rate, after accounting for closing costs. If the second loan is small, the blend may already be low enough that refinancing the whole thing adds cost. Compare the new rate against the blend, not against the higher of the two rates.