Should You Pay Off Your Mortgage or Invest?

Overpaying your mortgage delivers a guaranteed, risk-free return equal to your mortgage interest rate. If your rate is 5%, every pound of overpayment saves you 5% a year in interest you would otherwise pay — with no uncertainty and no tax to worry about, because the saving is not treated as income or a gain.

That certainty is worth a great deal. To beat it, an investment would need to earn more than your mortgage rate after charges and tax, consistently, over your time horizon. The higher your mortgage rate, the harder that is to achieve, which is why overpaying tends to look more attractive when borrowing is expensive and less attractive when rates are low. Reducing your mortgage also lowers your monthly outgoings and the total interest paid over the life of the loan, and it can bring valuable peace of mind as you approach retirement.

Investing offers the potential for higher long-term returns than a typical mortgage rate, particularly over periods of ten years or more. Historically, diversified investment in shares has tended to outpace mortgage rates over the long run — but this is a potential, not a promise, and values can fall as well as rise.

The key differences from overpaying are risk and time. Investments can drop sharply in the short term, and you could get back less than you put in, so this route suits money you will not need for several years. There is also the matter of liquidity: money invested in an ISA can be accessed if needed, whereas money used to overpay a mortgage is locked into your property and only released by remortgaging or selling. For many people, the ability to keep money accessible is a point in favour of investing.

The comparison changes once tax reliefs enter the picture. Pension contributions attract tax relief of 20% to 45%, and often an employer contribution on top, which can make paying into a pension more attractive than either overpaying the mortgage or investing outside a pension. For many people, capturing the full employer match should come before either option.

Investing within an ISA also improves the case for investing, because growth and withdrawals are tax-free. Outside these wrappers, returns can be reduced by dividend tax — now 10.75% at the basic rate and 35.75% at the higher rate for 2026/27 — and by capital gains tax above the £3,000 annual exempt amount. Mortgage overpayments, by contrast, produce a tax-free saving. Comparing like with like means looking at investment returns after tax, which narrows the gap with the guaranteed saving from overpaying.

Numbers are only part of the decision. Check whether your mortgage allows penalty-free overpayments — many let you overpay up to 10% of the balance each year, but exceeding that can trigger early repayment charges that wipe out the benefit. Fixed-rate deals in particular may restrict how much you can overpay.

Your emotional relationship with debt matters too. Some people sleep better with a smaller mortgage and are happy to accept a slightly lower expected return for that comfort; others are comfortable carrying a low-rate mortgage while their investments work. Neither is wrong. Flexibility is also worth weighing: an accessible investment pot can be drawn on in an emergency, whereas overpayments cannot easily be reversed.

While every situation is different, a widely used order of priorities can help frame the decision. First, clear any expensive short-term debt such as credit cards, where interest rates far exceed any mortgage or investment return. Second, build an accessible emergency fund of roughly three to six months' expenses. Third, secure any employer pension match, which is effectively free money.

Only after those foundations are in place does the mortgage-versus-invest question really come into focus — and even then, splitting spare money between the two is a perfectly reasonable middle path that captures some guaranteed saving and some growth potential. There is no rule that says you must choose only one.