What is a mortgage top-up?
A top-up increases an existing mortgage to release additional borrowing against the property. It can be useful for certain purposes, but it also increases the debt secured on your home.
Page checked: 21 October 2026
The key point
A top-up increases an existing mortgage to release additional borrowing against the property. It can be useful for certain purposes, but it also increases the debt secured on your home.
Top-up is not free money
A lower monthly cost than an unsecured loan can be misleading if the new borrowing is spread over a long mortgage term. Compare total interest and the purpose of the borrowing.
What can affect a top-up?
A lender normally looks at the purpose of the additional borrowing, your income and expenses, existing mortgage balance, repayment history, credit position and the value of the property. The amount you can raise is therefore not determined by a single percentage or salary multiple.
Your equity matters because the new borrowing remains secured against the property. A valuation may be required, and there can also be legal, valuation, administration or other lender-specific costs. If the top-up is used to consolidate other debts, compare the total cost carefully: spreading a shorter unsecured debt over a long mortgage term can make the monthly payment look smaller while increasing the amount of interest paid.
Questions to ask before applying
- How much additional borrowing would I actually qualify for?
- What rate and term would apply to the top-up?
- Will there be valuation, legal or administration costs?
- Will the top-up have a separate repayment or be combined with the existing mortgage?
- What would the total interest cost be if the borrowing runs for the full term?
For a broader affordability check, compare the figures with the mortgage affordability guide and the existing mortgage holders guide.
Keep checking the numbers
Use the mortgage top-up calculator examples to test different borrowing amounts, and compare a top-up with a personal loan before deciding what to investigate.
Use the calculators for your own balance, rate, term and affordability.
Open the calculators →Compare the monthly payment with the total cost
A top-up can look affordable when the additional borrowing is spread across a long term. The monthly payment alone does not show whether it is good value: the longer the debt remains outstanding, the more interest may be paid.
| Before applying | What to compare |
|---|---|
| Rate and term | Ask whether the top-up has its own rate or term, and whether those differ from your existing mortgage. |
| Total interest | Compare the expected total repayments, not just the monthly figure. |
| Fees | Check valuation, legal, administration or other charges that apply to your lender and case. |
| Security and risk | Remember that the extra borrowing is secured against your home; missed payments can put the property at risk. |
| Alternative borrowing | Compare a personal loan or saving up, where suitable, on both monthly payments and total cost. |
For a first comparison, use the top-up repayment examples and top-up versus personal loan guide. They are illustrations only; ask your lender for a personalised quote and confirm any conditions before committing.
Sources & important note
Information is for general information only. Mortgage rules, rates, lender criteria and costs can change. Always confirm the current position with the relevant lender or official source before making a financial decision.