Second charge mortgage calculator
Enter your home's value, your current mortgage balance and the amount you want to borrow to see the combined loan to value, an estimated monthly payment and the total cost of a second charge mortgage. Results are estimates from the rate you enter, not an offer.
Reviewed by David Sampson, Founder & Director · Created 19 October 2026 · Last reviewed 19 October 2026
How to use the second mortgage calculator
Enter your home's current value, what you still owe on your first mortgage, the amount you want to borrow, the term and an interest rate. The calculator shows the combined loan to value across both loans, the equity left, the estimated monthly payment and the total amount repayable at that rate.
This second mortgage calculator works as a second charge mortgage calculator for any loan secured behind an existing mortgage, whether you call it a 2nd charge loan or a second mortgage. Choose capital and interest to see a payment that clears the loan by the end of the term, or interest-only to see the interest cost alone, with the full amount still owed at the end.
Use an up-to-date estimate of the home's value, such as recent sale prices for similar homes nearby, and the current balance from your latest mortgage statement rather than the amount you first borrowed.
What combined loan to value means
Combined loan to value is the total of your first mortgage and the new second charge, shown as a percentage of your home's value. Lenders set a maximum combined loan to value, which limits how much you can borrow. The lower the figure, the more lenders are likely to consider the loan, often at lower rates.
For example, a home worth £300,000 with a £150,000 first mortgage and a £30,000 second charge has a combined loan to value of 60%, leaving £120,000 of equity (example figures, not market data). The guide to second charge mortgages explains how lenders use this figure alongside credit history.
Lenders also test whether you can afford both payments from your income and outgoings. The calculator does not check affordability, so a loan that fits on loan to value may still be smaller once a lender has looked at your budget.
Reading your results
The monthly payment and total repayable assume the rate stays the same for the whole term, which is rarely the case. Fees are not included unless you add them to the loan amount. Use the results to compare scenarios, such as a shorter term or a smaller loan, then check real offers against a dated illustration.
Running a few scenarios side by side shows the trade-offs quickly. A longer term lowers the monthly payment but raises the total interest, and a smaller loan can bring the combined loan to value into a lower band. To see what drives pricing, read the page on second charge mortgage rates before choosing a rate to enter.
The results are an estimate at the rate you enter, not an offer. A lender's illustration shows the actual rate, fees, APRC and total amount repayable for your case.
What is a second charge mortgage?
A second charge mortgage is a separate loan secured on your home behind your existing mortgage, so you can borrow against your equity without remortgaging. You make two monthly payments, and the first lender is repaid first if the home is sold. Your home may be repossessed if you do not keep up repayments.
People use these loans to fund home improvements, consolidate debts or raise money while keeping a low first-mortgage rate. The guide to second mortgages covers how to get one and the alternatives to compare first.
Frequently asked questions
How much can I borrow on a second charge mortgage?
It depends on your equity, income and credit history. Lenders set a maximum combined loan to value across both loans, and they also check you can afford both monthly payments. The calculator shows the combined loan to value for any amount you enter, which helps you test what may be possible before applying.
What interest rate should I enter?
Enter a rate from a recent quote or illustration if you have one. If not, the dated table on the second charge mortgage rates page gives a guide to current pricing. Try a few rates, including a higher one, to see how sensitive the payment is to the rate you are eventually offered.
Does the calculator include fees?
No, not unless you add them to the loan amount. Second charge loans can carry arrangement, valuation, legal and broker fees, and some can be added to the loan, which means paying interest on them. Adding expected fees to the amount gives a more realistic monthly payment and total repayable.
What is a good combined loan to value?
There is no single figure, because each lender sets its own limits. In general, a lower combined loan to value means more lenders are likely to consider the loan and pricing tends to be lower. The calculator shows how the figure changes as you adjust the amount you borrow.
Can I use the calculator for an interest-only loan?
Yes. Choose interest-only to see the monthly interest cost, which is the loan amount multiplied by the rate and divided by twelve. The full loan is still owed at the end of the term, so lenders offering interest-only usually want to see a clear plan for repaying it.
Is the result a mortgage offer?
No. The results are an estimate at the rate you enter, not an offer or a quote. A lender works out what it will lend after checking your income, credit history and the property, and it gives you an illustration showing the actual rate, fees and total cost before you commit.
Important: Your home may be repossessed if you do not keep up repayments on your mortgage. Information on this page is for general guidance only and does not constitute financial advice.Always verify details directly and seek independent advice before making financial decisions.