Mortgage Debt Consolidation Calculator
Interest saved by rolling debt into a mortgage.
Compare total interest on high-rate debt kept separate versus consolidated into your mortgage — sometimes the lower rate isn't actually cheaper.
What this tool does
This calculator models the interest difference between two debt repayment paths: paying off existing debt on its current schedule versus rolling that debt into a mortgage. You enter the amount of debt to consolidate, its current interest rate and payoff timeline, plus your mortgage rate and term. The calculator then estimates total interest paid under each scenario and shows the difference. The result illustrates how consolidating into a lower-rate mortgage typically reduces total interest, though it extends repayment across the full mortgage term rather than retiring the debt sooner. The calculation assumes standard amortisation and does not account for fees, rate variations, early repayment options, or changes to your mortgage structure. This is an educational illustration of the interest trade-off involved in consolidation.
Enter Values
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Formula Used
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Disclaimer
Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.
Consolidating high-rate debt into a mortgage lowers the rate but stretches repayment. At 22% credit card rates vs a 5% mortgage, the rate gap looks overwhelming — but the trap is term length. 15,000 of credit card debt at 22% paid over 5 years costs about 9,800 in interest. Rolling into a 25-year mortgage at 5% costs about 11,300 in interest — a touch worse, despite the lower rate, because the debt sticks around five times longer. Keep the term short and consolidation can help; stretch it to the full mortgage and you lose.
How to use it
Enter debt amount, its current rate, the remaining years on it, and your mortgage rate. The tool shows total interest in each scenario and the saving or loss.
Run it with sensible defaults
Using debt to consolidate of 15,000, current debt rate of 22%, current payoff term of 5, mortgage rate of 5%, the calculation works out to 1,449.53. The defaults are meant as a starting point, not a recommendation.
The levers in this calculation
The inputs — Debt to Consolidate, Current Debt Rate, Current Payoff Term, Mortgage Rate, and Mortgage Term — do not pull with equal force. Not every input has equal weight. Adjusting one input at a time toward extreme values shows which ones move the result most.
How the math works
Standard amortisation applied to each scenario. Interest paid = total payments minus principal.
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.
Consolidating £15,000 at 22% into a 5% mortgage over 25 years years yields 1,449.53 in interest savings.
Inputs
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
Standard amortisation applied to each scenario. Interest paid = total payments minus principal.
Frequently Asked Questions
Why can consolidation lose money?
Can I consolidate without extending?
Are there other costs?
What about secured vs unsecured?
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