Combining a primary mortgage with a second or third lien affects total borrowing costs, and a Mortgage Blended Rate Calculator produces one weighted average rate across both loans.
Mortgage Blended Rate Calculator: Find Your Weighted Average Rate Across Multiple Home Loans
This mortgage blended rate calculator combines a primary mortgage with an optional second mortgage or HELOC, and an optional third lien, into a single balance-weighted interest rate, along with the combined loan-to-value ratio against your property’s estimated worth. It’s used by homeowners carrying more than one loan against the same property who want one combined rate and leverage figure to compare against a cash-out refinance or a new consolidated loan offer.
Entering Your Property Value and Each Loan’s Balance and Rate
Inputs are an estimated property value and, for the primary mortgage plus up to two subordinate loans, each loan’s current balance and nominal annual interest rate. Any individual loan’s balance can be left at $0 if it doesn’t apply, but at least one loan needs a balance above $0. Rates are treated as nominal annual percentages, not effective annual or compounded rates.
How the Weighted-Average Blended Rate and Combined LTV Are Calculated
The blended rate is a balance-weighted average of the nominal annual rates you enter for each loan, the standard method for combining rates across multiple concurrent loans:
$$BlendedRate = \frac{\sum_i B_i \times r_i}{\sum_i B_i} \times 100$$
where $B_i$ is each loan’s current balance and $r_i$ is its nominal annual rate as a decimal. This treats every loan’s stated APR identically regardless of how that specific loan actually compounds — a fixed-rate mortgage and a revolving HELOC are combined using their nominal rates alone, not an effective rate that accounts for each one’s own compounding frequency or remaining term.
A common input mistake is entering a monthly rate instead of the nominal annual APR for any one of the three loans, which understates that loan’s contribution to the blended rate by roughly a factor of 12.
The combined loan-to-value ratio follows the standard formula Fannie Mae’s Selling Guide uses for Combined Loan-to-Value (CLTV): the sum of the unpaid principal balances on the primary mortgage and any subordinate financing, divided by the property’s value.
$$CLTV = \frac{B_1 + B_2 + B_3}{V} \times 100$$
Fannie Mae’s guide divides by the lesser of the sales price or the appraised value; this calculator divides by whatever property value you enter, so treat CLTV as an estimate unless that figure reflects a current appraisal.
Note that this 80% CLTV benchmark, used here to size the “Room to 80% LTV” figure, is a widely used industry convention tied to conventional loan pricing and second-lien underwriting, not a fixed limit Fannie Mae applies to every loan — actual maximum allowable CLTV varies by loan program.
It’s also a different threshold from the Homeowners Protection Act’s 78%/80% PMI cancellation points, which apply only to a single first mortgage measured against its original property value, not a combined, multi-lien balance measured against a current estimate.
A property value of $0 is rejected outright, since it would divide by zero in the CLTV calculation, and every individual loan balance can be $0 — but total combined debt across all three must be above $0, since a blended rate is undefined with no debt at all.
If your combined balance exceeds 80% of the property value you entered, “Room to 80% LTV” shows $0 rather than a negative number, so check the CLTV percentage itself to see how far over that mark you actually are. Because these figures follow directly from the balances, rates, and property value you enter, treat them as estimates for comparing loan structures rather than as personalized lending or tax advice.
Debt Share vs. Interest Cost Share Between Your Primary and Subordinate Loans
Combined Loan-to-Value Formula and PMI Threshold References
| Reference item | Detail | Source and date |
|---|---|---|
| Combined Loan-to-Value (CLTV) formula | Sum of the unpaid principal balances of the first mortgage and any subordinate financing, divided by the lesser of the sales price or the appraised value of the property | Fannie Mae Selling Guide, Section B2-1.2-02, current edition published June 2026 |
| PMI cancellation thresholds (single first mortgage only) | Borrower-requested cancellation at 80% of the property’s original value; automatic termination at 78% of original value, provided the borrower is current on payments | Homeowners Protection Act of 1998, 12 U.S.C. §4901 et seq., per CFPB’s HPA compliance procedures |
These figures are U.S.-specific and federal. The CLTV formula applies broadly across mortgage underwriting; the PMI thresholds apply only to a single conventional first mortgage with no subordinate liens, which is a narrower scenario than the multi-loan CLTV this calculator produces.
Common Questions About Blending Rates Across Multiple Home Loans
Can I calculate a blended rate with only a primary mortgage and no second loan?
Yes. Leaving the second and third mortgage balances at $0 is valid; the blended rate calculation simply reduces to your primary mortgage’s own rate, since a $0 balance contributes nothing to the weighted average.
What happens if I forget to enter a real second or third mortgage balance?
Nothing is flagged as an error — a $0 balance is treated as “no loan there.” If you actually carry that debt but leave the field blank or at $0, the blended rate and CLTV will both understate your true combined position.
Why does “Room to 80% LTV” show $0 instead of a negative number?
That field is floored at $0 once your combined balance passes 80% of the property value, so it can’t go negative. Check the CLTV percentage directly to see exactly how far past 80% your combined debt actually sits.
Is the 80% LTV benchmark here the same as the PMI cancellation threshold?
No. This calculator’s 80% mark is a general CLTV underwriting convention across all your loans against a current value estimate. The Homeowners Protection Act’s 78%/80% PMI thresholds apply only to a single first mortgage measured against its original value.
Does the calculator account for each loan’s own compounding method?
No. It treats every loan’s entered rate as a nominal annual percentage and weights it only by balance, regardless of whether that loan compounds monthly, like a typical fixed mortgage, or daily, like many revolving HELOCs.
Does the currency selector convert my balances?
No. Choosing USD, INR, EUR, GBP, AUD, or CAD only changes the displayed symbol. The blended rate and CLTV math is identical no matter which currency is selected.