Calculate your monthly payment and total interest on a second charge mortgage, and check your combined loan-to-value ratio.
Rates as of Q2 2025 (example)
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A second charge mortgage calculator estimates the monthly payment and total interest on a second charge mortgage — a loan secured against your home in addition to your existing (first charge) mortgage. It also calculates your available equity and your combined loan-to-value (CLTV) ratio, which represents your total secured borrowing (both mortgages) as a percentage of your property's value.
Your available equity is your property value minus your existing mortgage balance. The combined loan-to-value (CLTV) ratio adds your existing mortgage balance and the new second charge loan together, expressed as a percentage of your property value — this represents your total secured debt against the property. The monthly payment is calculated using the standard amortising loan formula for the second charge loan amount, rate, and term.
Formula: Available Equity = Property Value − First Charge Mortgage Balance. CLTV % = [(First Charge Balance + Second Charge Loan) ÷ Property Value] × 100. Monthly Payment = [Loan Amount × r × (1+r)n] / [(1+r)n − 1], where r is the monthly interest rate and n is the number of months.
Example: For a £320,000 property with a £180,000 existing mortgage, available equity is £140,000. Taking a £30,000 second charge loan brings the combined loan-to-value to about 65.6% (£210,000 ÷ £320,000). At a 9.5% interest rate (example rate — enter your actual rate) over 15 years, the monthly payment is roughly £313. (Note: all figures in this example are for illustration purposes only and do not represent a loan offer.)
A second charge mortgage is a separate loan secured against your home, sitting "behind" your existing (first charge) mortgage — if the property were repossessed and sold, the first charge lender would be repaid first, with the second charge lender repaid from any remaining proceeds, which is why second charge rates are typically higher than first charge mortgage rates. Second charge mortgages are sometimes used for home improvements, debt consolidation, or other large expenses, particularly when remortgaging the entire first charge mortgage wouldn't make sense — for example, if you're on a good fixed rate with an early repayment charge that would apply if you remortgaged. Like any loan secured against your home, missing payments puts your home at risk, so it's important to compare second charge mortgages against alternatives, including a further advance from your existing lender, remortgaging, or unsecured personal loans, which may be more suitable depending on your circumstances.
A first charge mortgage is your primary mortgage, with the first claim on your property if it's repossessed and sold. A second charge mortgage is an additional loan secured against the same property, with a claim that ranks behind the first charge mortgage — this additional risk to the lender is one reason second charge rates are typically higher.
Combined loan-to-value (CLTV) is your total secured borrowing — both your first charge mortgage and any second charge mortgage — expressed as a percentage of your property's current value. Lenders use CLTV to assess risk when considering a second charge mortgage application.
Second charge lenders rank behind the first charge lender if a property is repossessed and sold, meaning they take on more risk of not being fully repaid. This additional risk is generally reflected in higher interest rates compared to first charge mortgages.
It depends on your circumstances. A second charge mortgage can make sense if remortgaging your entire first charge mortgage would trigger an early repayment charge or mean losing a favourable existing rate. Remortgaging the whole amount might offer a lower overall rate if you're not tied into your current deal. Compare both options, including all fees.
No — the default is an example only. Second charge mortgage rates vary by lender, your credit profile, the CLTV ratio, and loan amount. Enter the actual rate from a quote for an accurate estimate.
Since a second charge mortgage is secured against your home, missing payments puts your home at risk of repossession, just as with your first charge mortgage. Always carefully consider your ability to afford both mortgage payments before taking out a second charge loan.
Disclaimer: The information, rates, and figures provided on this page are for educational and illustrative purposes only and do not constitute a loan offer or financial advice. The default interest rate is a sample value and does not reflect rates currently available from any specific lender. Your home may be repossessed if you do not keep up repayments on a mortgage or other loan secured against it. Second charge mortgage rates, fees, and terms vary by lender and depend on your individual circumstances. Always consult a qualified mortgage broker or financial adviser before taking out a loan secured against your home.