Blended Rate Mortgage Calculator
Two mortgages, one effective rate. Whether it is an 80-10-10 piggyback, a first mortgage plus a HELOC, or a jumbo-avoidance split, enter each loan’s balance and rate: the calculator returns the balance-weighted blended rate, each loan’s monthly payment, the combined payment, and the total interest across all loans.
Each loan’s payment is amortized at its OWN rate and summed. The blended rate is a weighted average of the rates, not the rate of the combined payment. The tool blends up to three loans, assumes the same term for all loans and fixed rates, and does not include taxes, insurance, or PMI.
Quick Answer
A $400,000 first mortgage at 6.5% plus a $100,000 second at 8.5% blends to 6.90%: (400,000 × 6.5 + 100,000 × 8.5) ÷ 500,000. The loans bill separately at $2,528.27 and $768.91 for a $3,297.19 combined payment and $686,986.81 total interest over 30 years.
Key takeaways
- The blended rate is a balance-weighted average of the rates, never a simple average. A small second loan at a high rate moves the blend only a little.
- Each loan’s payment is amortized at its OWN rate and summed. No lender charges you the blended rate: the blended rate is a comparison number, not a bill.
- The tool blends up to three loans, assumes one term for all of them and fixed rates, and leaves taxes, insurance, and PMI out of the math.
- Piggybacks exist mainly to dodge PMI or jumbo pricing. Whether one wins depends on the rate spread, the PMI quote, and how long you keep the second loan.
- Quick Answer
- How to use the blended rate mortgage calculator
- The blended rate formula: a weighted average, not a simple mean
- Worked example: the $400,000 + $100,000 loan stack
- The blended rate is a comparison tool, not a bill
- Why piggyback at all: dodging PMI and jumbo pricing
- What this calculator covers, and why each part matters
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the blended rate mortgage calculator
Enter each loan’s balance and rate, pick one term, and read the blend. The results stay hidden until you calculate, and the fields come pre-filled with the worked example.
- Enter the first loan amount and rate: the primary mortgage. Both are required, and the rate cannot be negative.
- Enter the second loan amount and rate: the second mortgage or HELOC. Also both required.
- Add a third loan only if you have one: leave both third-loan fields blank for a two-loan blend. Entering a third amount without its rate shows the message “Enter the third loan rate.”
- Pick the loan term: 30, 20, or 15 years. The same term applies to every loan in the blend.
- Click Calculate blended rate: the blended rate appears at the top, followed by the total borrowed, each loan’s payment, the combined payment, the total interest, and the formula the tool used.
Invalid entries are rejected with a plain message: a blank first amount (“Enter the first loan amount.”), a zero or negative balance (“First loan amount must be greater than zero.”), a negative rate (“First loan rate cannot be negative.”), and a negative third amount (“Third loan amount cannot be negative.”).
The blended rate formula: a weighted average, not a simple mean
The blended rate weights each loan’s rate by its share of the total debt. A simple average of 6.5% and 8.5% would say 7.5%; the true blend is 6.90%, because the bigger, cheaper loan dominates.
Each payment = balance × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1), where r is the monthly rate and n is the number of monthly payments.
The same weighted-average math works for any loans, not just mortgages: the blended rate calculator runs it for general loan blends, and the average interest calculator covers broader rate averages. What makes this page mortgage-specific is the piggyback structure around it: separate amortized payments per loan, a combined payment, and lifetime interest, so the structure can be judged against a single loan.
Worked example: the $400,000 + $100,000 loan stack
The worked example is pre-filled: a $400,000 first mortgage at 6.5%, a $100,000 second at 8.5%, 30 years. Click Calculate and the tool returns:
- Blended rate: (400,000 × 6.5 + 100,000 × 8.5) ÷ 500,000 = 3,450,000 ÷ 500,000 = 6.90%
- First loan payment: $400,000 at 6.5% over 360 months = $2,528.27/month
- Second loan payment: $100,000 at 8.5% over 360 months = $768.91/month
- Combined payment: $2,528.27 + $768.91 = $3,297.19/month
- Total interest over 30 years: $3,297.19 × 360 − $500,000 = $686,986.81
Where the combined payment comes from
That 76.7/23.3 split is the same story the blended rate tells: the first loan is 80% of the debt, so the blend sits much closer to 6.5% than to 8.5%. Change either balance and both the blend and the split move with it.
The blended rate is a comparison tool, not a bill
No lender charges you 6.90%. The first loan bills $2,528.27 and the second $768.91, often through different servicers, and each payment is amortized at its own rate. The blended rate exists to compare structures: is this two-loan setup cheaper than one $500,000 loan at 7% plus PMI? Run both and compare the combined payment and the total interest. That comparison is the entire point of the number. To price the single-loan alternative, the mortgage payment calculator gives you its payment and lifetime interest in one click. If refinancing is the alternative you are weighing instead, the cost to refinance mortgage calculator totals the closing costs that decide whether the switch pays.
Why piggyback at all: dodging PMI and jumbo pricing
Two reasons dominate, and both are about what the second loan lets you avoid.
First, avoiding PMI. With less than 20% down on a conventional loan, lenders require private mortgage insurance. Freddie Mac puts the cost at roughly $30 to $70 a month for every $100,000 borrowed. Keeping the first mortgage at exactly 80% loan-to-value sidesteps it: the classic 80-10-10 structure on a $500,000 purchase is a $400,000 first mortgage, a $50,000 second, and $50,000 down. At 6.5% and 8.5%, that 80-10-10 stack blends to 6.72%. PMI, meanwhile, drops off once you reach 20% equity, while second-lien interest lasts until you pay the loan down, which is why the piggyback usually wins only if you clear the second loan in a few years.
Second, dodging jumbo pricing. Keeping the first mortgage under the Federal Housing Finance Agency’s conforming loan limits avoids jumbo-loan pricing and stricter qualifying rules. A piggyback second can be the difference between a conforming first and a jumbo one.
Piggyback (two loans)
- No PMI when the first loan stays at 80% loan-to-value
- Second lien’s higher rate is the price you pay
- Second lien lasts until you pay it down
- Refinancing later needs both lenders to agree
- Conventional loans only, not FHA, VA, or USDA
Single loan + PMI
- One payment, one servicer, simpler paperwork
- PMI of roughly $30 to $70 a month per $100,000 borrowed
- PMI ends once you reach 20% equity
- Refinancing needs only one lender’s agreement
- Works on government-backed loans too
There is no universal winner: it depends on the rate spread, the PMI quote, and how long you keep the loans. A piggyback converts a non-deductible insurance premium into interest on the second lien, which may be deductible subject to IRS limits, and the Consumer Financial Protection Bureau’s own piggyback guidance stresses comparing the two structures’ total costs before choosing. Piggybacks need strong credit, and if home values fall you can owe more than the home is worth across both liens, which makes refinancing either loan harder.
What this calculator covers, and why each part matters
This calculator blends up to three mortgages into one comparison number, with each loan’s own payment and the lifetime cost shown beside it.
- Up to three loans, not two. Each loan’s payment is amortized at its own rate and shown separately, then summed: on the worked example, a $400,000 first mortgage at 6.5% and a $100,000 second at 8.5% bill separately at $2,528.27 and $768.91, for a $3,297.19 combined payment.
- The blended rate, done as a weighted average. (400,000 × 6.5 + 100,000 × 8.5) ÷ 500,000 = 6.90%. The first loan is 80% of the debt, so the blend sits much closer to 6.5% than to 8.5% — and the 76.7/23.3 payment split tells the same story.
- Lifetime interest beside the monthly figure. The same example costs $686,986.81 in total interest over 30 years, so the structure can be judged against a single loan, not just month to month.
- The piggyback framing, not just the arithmetic. Piggybacks exist mainly to dodge PMI or jumbo pricing, and whether one wins depends on the rate spread, the PMI quote, and how long you keep the second loan.
- The honesty line, kept. The blended rate is a weighted average, not a bill: no lender charges it. The tool assumes one term for all loans and fixed rates, and leaves taxes, insurance, and PMI out of the math.
If you are weighing a piggyback against paying PMI instead, the mortgage PMI calculator prices that alternative.
Frequently asked questions
Balance-weighted average: multiply each loan balance by its rate, add those products, and divide by the total balance. A $400,000 loan at 6.5% plus a $100,000 loan at 8.5% blends to (400,000 × 6.5 + 100,000 × 8.5) ÷ 500,000 = 6.90%.
No. Each loan bills separately at its own rate, often through different servicers, and each payment is amortized at that loan’s own rate. The blended rate is a weighted average of the rates, not the rate of the combined payment. It exists to compare loan structures, not to describe a bill you will receive.
An 80% first mortgage, a 10% second mortgage, and 10% down payment: two loans that keep the first at 80% loan-to-value to avoid private mortgage insurance. On a $500,000 purchase, that is a $400,000 first mortgage, a $50,000 second, and $50,000 down.
Often, but not always. Compare the combined two-loan payment against a single loan plus PMI. Freddie Mac puts PMI at roughly $30 to $70 a month for every $100,000 borrowed, and PMI drops off once you reach 20% equity, while second-lien interest lasts until you pay the loan down. Borrowers who expect to clear the second lien in a few years usually favor the piggyback.
Subordinate position means more lender risk. In foreclosure, the first lien is paid first and the second lien gets what is left, so the second lender charges more for the extra risk.
Yes. As the loans amortize at different speeds, the balance weighting shifts, so the blend drifts from the origination snapshot this tool computes. Recalculate whenever a balance changes materially.
This tool assumes one term for all loans and fixed rates. With different terms, amortize each loan separately over its own term and weight the rates by the balances, rather than using a single term for the whole stack.
Yes. It runs entirely in your browser, needs no account, and stores nothing. Copy the result with “Copy my results” or send it to another app with “Share results”.
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References
- Consumer Financial Protection Bureau. What is a “piggyback” second mortgage? (piggyback definition, comparing against a single loan with mortgage insurance, and the added difficulty of refinancing with two lenders). Accessed October 24, 2026.
- Consumer Financial Protection Bureau. What is mortgage insurance and how does it work? (mortgage insurance protects the lender, not the borrower, and the 80% loan-to-value threshold). Accessed October 24, 2026.
- Consumer Financial Protection Bureau. What is private mortgage insurance? (PMI on conventional loans with less than 20% down, and cancellation at 20% equity). Accessed October 24, 2026.
- Internal Revenue Service. Publication 936, Home Mortgage Interest Deduction (interest deductibility limits for home mortgage debt, including second liens). Accessed October 24, 2026.
- Freddie Mac, My Home. Breaking down PMI (PMI costs of roughly $30 to $70 per month for every $100,000 borrowed). Accessed October 24, 2026.
- Board of Governors of the Federal Reserve System. A Consumer’s Guide to Mortgage Refinancings (amortization and the total cost of refinancing a mortgage). Accessed October 24, 2026.
- Federal Housing Finance Agency. FHFA Announces Conforming Loan Limit Values for 2026 (the conforming loan limits that separate conventional loans from jumbo loans). Accessed October 24, 2026.
- Consumer Financial Protection Bureau. What is a Qualified Mortgage? (ability-to-repay and qualified mortgage standards that govern piggyback underwriting). Accessed October 24, 2026.
- Consumer Financial Protection Bureau. What is a home equity line of credit (HELOC)? (HELOCs as open-end second liens secured by home equity, with draw and repayment periods). Accessed October 24, 2026.
- Consumer Financial Protection Bureau. What is the difference between a Home Equity Loan and a Home Equity Line of Credit (HELOC)? (both count as second mortgages payable in addition to the first mortgage). Accessed October 24, 2026.