The mathematics of mortgage overpayment are straightforward: every pound paid off early saves approximately four pounds in interest over a typical 25-year term. At current rates, the saving is even larger. Yet the majority of mortgage holders who have the financial flexibility to overpay do not do so.
How Overpayments Work
Most mortgages allow overpayments of up to 10% of the outstanding balance per year without early repayment charges. On a £250,000 mortgage, that is up to £25,000 per year — far more than most households can realistically afford. The relevant comparison is between the interest saved on the mortgage and the return available on savings or investments.
The Calculation
At a mortgage rate of 4.5% and a savings rate of 4.8%, the financial difference is marginal — and slightly favours keeping money in savings. But at a mortgage rate of 5.5% and a savings rate of 4.2%, the mortgage overpayment is clearly superior.
This calculation changes every time your mortgage rate or savings rate changes. Review it regularly.
Beyond Overpayments: Other Strategies
Reducing your mortgage term — accepting a higher monthly payment in exchange for a shorter loan — can save enormous sums over time. Moving from a 25-year to a 20-year term increases monthly payments by approximately 12% but reduces total interest by 25–30%.
Remortgaging at the right time matters enormously. Being organised enough to review your deal three to six months before your current fix expires ensures you avoid rolling onto the standard variable rate, which is typically 1–2% higher than available fix rates.
