Why Lower Rates Can Cost More
It sounds counterintuitive, but a lower interest rate doesn't always mean a lower total cost. The key factor is time. When you add debt to your mortgage, you're typically extending the repayment period from a few years to 20 or 30 years. Interest compounds over this much longer period, and even a low rate adds up substantially.
Think of it this way: paying 5% interest for 25 years accumulates far more total interest than paying 15% for three years. The monthly payments at 5% are lower, which is why people are attracted to the idea, but the overall bill is bigger. This is the fundamental trade-off at the heart of debt consolidation remortgages.
Worked Examples
Let's compare £20,000 in debt under different scenarios:
- Credit cards at 22% APR, repaid over 3 years: monthly payment ~£760, total interest ~£7,400, total repaid ~£27,400
- Personal loan at 7%, repaid over 5 years: monthly payment ~£396, total interest ~£3,800, total repaid ~£23,800
- Added to mortgage at 5%, repaid over 25 years: monthly payment ~£117, total interest ~£15,000, total repaid ~£35,000
The mortgage option costs nearly £12,000 more than repaying the credit cards over three years, and over £11,000 more than the personal loan — despite having by far the lowest interest rate. The monthly payment is also the lowest, which is the trade-off many people are willing to make.
How to Minimise the Extra Cost
The good news is that you can dramatically reduce the long-term cost of consolidation by overpaying your mortgage. If you direct even a portion of your monthly savings towards overpayments, you'll clear the extra borrowing much faster and pay far less interest.
Using our example: if you added £20,000 to your mortgage but overpaid by £300 per month (still less than the original credit card payments of £760), you'd clear the extra borrowing in about 5 years and pay roughly £2,600 in interest — less than any of the other options. This is the optimal approach: consolidate for the lower rate, then overpay to shorten the term.
The Break-Even Point
There's a point at which consolidation becomes cost-effective compared to keeping the original debts. This depends on how aggressively you overpay. As a general rule, if you can clear the extra mortgage borrowing within the same timeframe as you would have repaid the original debts, consolidation saves you money because of the lower interest rate.
If you consolidate and make no overpayments at all, letting the debt run for the full mortgage term, you'll almost certainly pay more overall. The decision comes down to discipline: are you committed to overpaying, or will the lower monthly payment tempt you to spend the savings elsewhere?
Important: Your home may be repossessed if you do not keep up repayments on your mortgage. There will be a fee for mortgage advice. The actual rate available will depend on your circumstances. Think carefully before securing other debts against your home.