FinToolSuite

Piggyback Mortgage Calculator

Updated April 17, 2026 · Mortgage · Educational use only ·

80-10-10 vs conventional: avoid mortgage insurance.

Compare piggyback 80-10-10 mortgage cost against single loan with mortgage insurance. Enter property price and deposit for an instant result.

What this tool does

Enter property price, rates, and terms. The tool shows combined payment and comparison against a conventional loan.


Enter Values

Formula Used
First loan payment
Second loan payment

Spotted something off?

Calculations, display, or translation — let us know.

Disclaimer

Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.

400,000 home with 10% down: 80% first mortgage (320,000 at 5%) + 10% second mortgage (40,000 at 7.5%) + 10% deposit. Combined payment 2,000/month avoids mortgage insurance required on single 90% LTV loans. Second loan upper rate but saves PMI.

A worked example

Try the defaults: property price of 400,000, deposit of 10%, first loan of 80%, first loan rate of 5%. The tool returns 1,997.51. You can adjust any input and the result updates as you type — no submit button, no reload. That's the real power here: seeing how sensitive the output is to one or two assumptions.

What moves the number most

The result responds to Property Price, Deposit %, First Loan %, First Loan Rate, and Second Loan Rate. Not every input has equal weight. Flip one at a time toward extreme values to feel which ones move the needle most for your situation.

The formula behind this

Two amortisations combined. Everything the calculator does is shown in the formula box below, so you can check the math against your own spreadsheet if you want.

Why this matters before you sign

A mortgage is usually the biggest single financial commitment a person makes. The difference between a well-chosen product and a hasty one can run into tens of thousands over the life of the loan. Running the numbers here before committing is the cheapest form of due diligence available.

What this doesn't capture

The figure excludes arrangement fees, valuation costs, legal fees, insurance, and any early-repayment charges — those can add several thousand to the headline cost. Rate changes at renewal for fixed-term deals will shift the picture further. Use this for the core interest/principal math and add the other costs on top.

Example Scenario

Piggyback mortgage produces combined payment figures based on the inputs provided.

Inputs

Property Price:400,000 £
Deposit %:10
First Loan %:80
First Loan Rate:5
Second Loan Rate:7.5
Term:30
Expected Result£1,997.51

This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.

Sources & Methodology

Methodology

Two amortisations combined.

Frequently Asked Questions

Why piggyback?
Avoids private mortgage insurance (PMI) required on loans above 80% LTV. Second loan at upper rate but no PMI.
When does it save money?
When second-loan interest is less than PMI you'd pay on combined loan. Depends on rates and deposit size.
Still available?
Less common post-2008. Some lenders offer. Equivalent: shared equity schemes.
Risk?
Two loans, two sets of fees, refinance complication if one changes terms. Not always cheaper long-term.

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