Estimate the monthly cost of a second charge before you apply
A second charge sits behind your existing mortgage, secured on the same property, funded out of equity you already hold. The first mortgage carries on untouched. Our second charge mortgage calculator gives you the monthly cost of that new borrowing, at whatever amount, term and rate you want to test.
It stops there, though. Whether a lender will release the sum you have typed in is a separate question, and the equity maths below answers it. Whether the payment works alongside everything else you owe is a third question, and that one needs someone looking at your actual commitments.
How to use the second charge mortgage calculator
The tool is shared across our calculator range, so the labels talk about buying rather than borrowing. Where it says Purchase Price, type the sum you want to raise. Where it says Down Payment, put nothing, because a second charge takes no deposit. Set the Term to the number of years you want the loan to run, and pitch the Interest Rate above your current mortgage rate, since second charge money costs more than first charge money.
Press Calculate and you get the repayment on the new loan by itself. Your existing mortgage payment carries on unchanged on top of it.
Feel free to use our Finance Calculator
**Note: For exceeding 120 no. of payments, a group of 12 payments will be combined into a single payment number for better chart visibility.
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Working out what you can actually release
Lenders govern this with combined loan to value: your current mortgage plus the proposed second charge, set against what the property is worth.
Each lender draws its own line. Owner-occupied houses reach the highest bands. Investment property and business-purpose borrowing sits lower, because a second charge lender only gets paid once the first charge lender has been paid in full, and that risk has to be priced somewhere.
Getting to the figure is simple arithmetic. Take the value of the property, apply the lender’s ceiling to it, then knock off the balance outstanding on your first mortgage. What is left is your headroom, on paper at least.
A £60,000 extension on a £420,000 house
Take an owner-occupier whose home is worth £420,000. There is £252,000 left on the mortgage, so 60% loan to value and £168,000 of equity sitting behind it.
Their lender draws the line at 85% combined, which caps total secured debt on the property at £357,000. Deduct what the first charge already uses and £105,000 remains reachable.
The extension needs £60,000. That lifts everything owed to £312,000, or 74% combined, well under the ceiling. Spread across fifteen years at 9.5%, the second charge costs roughly £627 a month. Interest over the full term comes to about £52,800.
A £50,000 deposit raised on a rental
Investment property is capped tighter, and that single difference does most of the work here.
The property is worth £300,000 with £165,000 of buy to let borrowing against it. Equity stands at £135,000, but a 75% ceiling allows total debt of only £225,000, so £60,000 is what can genuinely be reached rather than the full £135,000.
The landlord draws £50,000 toward the deposit on the next purchase. Total borrowing reaches £215,000, or 72%. Over ten years at 10.5% the payment lands near £675 a month, and interest adds up to something around £31,000.
Rates here are for illustration and are not quotes. Ceilings differ between lenders, rates move, and your own figure depends on the case you put in front of them.
What decides the amount a lender will release
Headroom on paper is the starting point, not the answer. Lenders then look at:
- Affordability. The new payment is assessed alongside your existing mortgage and other commitments, not in isolation.
- Purpose. Raising capital for home improvements, a tax bill or business investment are all common and accepted. Some purposes attract more scrutiny than others.
- Property type. Owner-occupied houses reach the highest ceilings. Flats, houses in multiple occupation, mixed-use and commercial property are all assessed on tighter terms.
- Credit history. Adverse credit narrows the panel and moves the rate rather than closing the door, because the equity carries much of the risk. Our adverse credit mortgages page covers how lenders weigh this.
- Term. A longer term lowers the monthly payment and raises the total interest paid. The examples above show the size of that trade.
- Valuation. The lender values the property themselves, and their figure is what governs the calculation.
Where the calculator stops and a broker starts
The estimate above tells you what a given amount costs each month. It cannot tell you which lenders will look at your case, what ceiling they apply to your property type, or how the application should be structured to get through underwriting cleanly.
Commercial Finance Network works across the full second charge panel. Before you apply anywhere, we will tell you what is realistically available against your equity and what it will cost. The second charge mortgage page sets out how the product works and who it suits.
Frequently Asked Questions
Why does the calculator ask for a purchase price and deposit?
This second charge mortgage calculator is a general repayment estimator shared across our calculator range.
Enter the amount you want to raise in the purchase price field and set the deposit to zero, and the monthly figure returned will be correct for a second charge.
Does the calculator show how much equity I can release?
No. It estimates repayments on an amount you choose.
Use the combined loan to value method set out above to work out the headroom first, then enter that figure.
Is the monthly figure my total mortgage cost?
No. It covers the second charge alone.
Your existing first mortgage payment continues unchanged alongside it, which is the point of a second charge rather than a remortgage.
What combined loan to value can I expect?
It depends on the property and the purpose.
Owner-occupied residential reaches the highest bands and investment property is capped lower. We will confirm the realistic ceiling for your case before an application goes anywhere.
Final Thoughts
A second charge mortgage calculator gives you a number. Whether that number is achievable depends on your equity, your income, the property and the lender, and those four things are best assessed together rather than one at a time.
Commercial Finance Network is a whole-of-market commercial finance broker supporting homeowners, property investors and businesses across the UK and internationally. We are directly authorised and regulated by the Financial Conduct Authority.
Think carefully before securing other debts against your home. Your home may be repossessed if you do not keep up repayments on your mortgage. Second charge lending taken for business purposes or secured against investment property is not regulated by the Financial Conduct Authority.
Call us on +44 1494 622 111 or email info@cfnuk.com to speak to a specialist directly.
Related Pages
- Second Charge Mortgage – How the product works, who it suits, and what lenders look for.
- Consolidating Debt into a Mortgage – Where secured consolidation helps a business and where it defers the problem.
- Second Charge Lending in Complex Ownership Structures – How trusts, LLPs and SPVs change the underwriting.
- Commercial Mortgage Rates – Current rate ranges by loan to value band, property type and borrower profile.
- Bridging Loan – Short-term property-secured lending where speed matters more than term.