Overpay Your Mortgage or Invest? How to Decide Where Your Money Works Harder

Rob Morgan is chief investment analyst at Charles Stanley.

For homeowners with a mortgage, a familiar money question often arises: should spare cash be used to reduce the loan, or would it be better put into investments?

The question may sound straightforward, but the right answer varies widely depending on personal circumstances, including your age, employment position, mortgage terms, interest rate and, crucially, how comfortable you are with risk.

With household costs still putting pressure on many budgets, not everyone will have surplus money available. But if you do — either now or later — it is worth weighing the key factors and asking the right questions before deciding what to do.

Paying off your mortgage: Safety first?

What is clear is that reducing your mortgage sooner can cut the total interest bill by thousands of pounds.

Each mortgage payment is typically split into two parts: interest charged on the borrowing, and a repayment of the original loan amount, often referred to as the principal.

The longer the mortgage runs, and the higher the interest rate, the more interest you will pay overall. This effect is most pronounced in the early stages, when the outstanding balance is larger and a greater share of each payment goes toward interest rather than reducing the debt itself.

Yet overpaying your mortgage – paying more than you need to under the terms of the loan agreement – comes with an ‘opportunity cost’.

In other words, had you invested the money could you have achieved a return in excess of the interest on the debt?

At higher mortgage interest rates there is arguably less of an opportunity cost. It is one thing bettering a 2 per cent or 3 per cent rate with investment returns, but achieving upwards of 6 per cent consistently is much more difficult.

The higher interest rates are the more it makes sense to repay debt as quickly as possible. That’s why high interest debts such as credit cards or personal loans should be repaid as a priority.

However, there can be such a thing as ‘good debt’. 

High inflation can mean your debt erodes away in relation to prices and your earnings, providing you keep up the repayments. 

Meanwhile, the current environment of rising interest rates is a worry for many mortgage holders, but much depends on the trajectory of interest rates in the future, not just the next couple of years.

If inflation and interest rates stay high over the medium to longer term, then reducing debt is likely to be wise.

However, it is also possible rates could come down quite sharply and the cost of mortgage debt returned to the low levels we have experienced for the past decade or so.

The good news is that inflationary pressures appear to be easing. When clear evidence emerges these are on a moderating trend, central banks can ease off hiking interest rates to tame runaway prices.

Those applying for mortgages now, as well as those on variable rates, may face an uncomfortable period of higher repayment costs, but this might well abate in the medium term.

If you do decide to pay down or pay off a mortgage you must consider any penalties for doing so. 

Early-repayment charges often apply during any fixed or discounted period and are usually calculated as a percentage of the amount you repay.

Often, these are tiered and fall away over time. 

Depending on circumstances, it can be worth paying an ERC as the interest saving could be more than the fee incurred. 

My verdict: Although many people would consider it an inferior route from a mathematical perspective, prioritising a smaller mortgage over investing can make your financial position more resilient.

It may give you greater control and more options, and it could reduce anxiety about an uncertain future.

Plus when you overpay your mortgage, the debt will shrink and you will have more disposable income, which could fund contributions into pensions or other investments. 

Investing your spare cash: Prioritise your pension

Building wealth over decades by allocating capital to well managed and growing companies has, historically at least, been a reliable way to grow wealth.

However, to fully harness the power of the stock market and enjoy the benefit of compounded returns, you need to leave your money invested for a long time – an absolute minimum of five years but ideally decades.

An important factor that might tilt the balance in favour of investing over paying down your mortgage is if you can get a significant leg up on the money you put in.

In this regard, using a pension scheme really stands out. Pension contributions benefit from tax relief which can ‘supercharge’ your returns.

Basic rate tax relief, for instance, adds 25 per cent to the value of your pot, and for higher rate taxpayers there is an even larger boost.

If you have access to a workplace pension, your employer will pay in too, making it a really cost effective method to save for retirement.

This should be maximised to the greatest extent possible before investing elsewhere.

Some investors use this strategy to help pay off their mortgage, but you need to bear in mind that money in a pension can’t be accessed until a minimum age is reached.

That’s 55 at present for personal pension schemes, but it is set to rise to 57 in 2028.

Bear in mind too that pension rules, and tax relief, can change in the future. The longer you have to invest the more beneficial the investing route might be, especially when it comes to pensions. 

My verdict: If you are happy taking risk, compounding investment returns over lengthy periods and investing as much extra money as possible can be a hugely powerful force.

That is provided your investment strategy is sound, and you have a long enough runway ahead to deal with the inevitable volatility markets throw at you. 

To overpay your mortgage or invest? It’s not just about the maths…

The answer to this quandary doesn’t necessarily lie in a spreadsheet.

Although investing may generate higher returns than a loan’s interest cost, markets also come with the risk of losses. That uncertainty is a factor in itself.

The peace of mind of lowering mortgage expenses and not having to worry about the performance of financial markets may outweigh the potential advantages of investing.

If your broader finances are in good shape – essentially that you don’t have other high interest debts to pay off and you have built up a fund for emergencies of around six months’ expenditure – both strategies can work well.

You can also split the difference and overpay your mortgage and pile more money into your investments, ideally via a pension, at the same time. 

Final checklist: What to consider before you decide

Your age: The longer you have to invest the more beneficial it can be. Younger investors tend to have decades in front of them meaning they can take more risk in pursuit of higher returns. 

However, those looking to clear the mortgage in the run up to retirement don’t have as long, so are more likely to err on the side of safety.

Your job status: If you are in a secure job with good prospects for earning more money in the future, you are likely to be more confident in relation to rising mortgage interest. 

Those in less secure employment or self employment might want to lower the interest burden and clear the debt quicker as the outlook is less certain.

Your mortgage terms and the interest rate: Those who have secured mortgage rates close to, or below, current interest rates are in a favourable position. 

However, if you are re-mortgaging or moving from a fixed to a standard variable rate, and therefore facing a sudden jump in payments, now could be an opportune time to pay off a chunk of debt to help make things more manageable. 

The higher interest rate on the debt represents a higher hurdle for investing that money instead.

If you are on a fixed rate: There are often penalties for paying off chunks of a fixed rate mortgage, so check the terms carefully. 

Those that have locked into fixed rates at the start of this year, or earlier, have likely secured a very competitive deal in relation to those available today, but think about when your fix finishes and what you will do at that point, especially if it is a shorter term two or three year deal.

Are you are a risk taker or more risk averse: If any financial decision means you lose sleep at night with worry then take the safe option.

Never put yourself in a vulnerable position if you can avoid it. 

The feeling of having a smaller mortgage and lower repayments can be reason in itself to repay debt, even though in the longer run investing might be more financially rewarding and the route those  who can afford to take the risk choose.