Should you overpay your mortgage or invest the extra money? A UK guide for higher earners

You've got spare money left over at the end of the month – so what do you actually do with it? Overpay the mortgage, top up an ISA, or put it into your pension?

Most guides give you a generic rule of thumb. This one doesn't. It's written for working women who are the main or joint financial decision maker in their household, and it covers the actual maths, the priority that usually gets missed, and what changes if your mortgage is jointly held.

Which one wins on the numbers

The honest answer is that it depends on your mortgage rate, and right now the gap between the two options is narrower than it has been in years. The average two year fixed mortgage rate in the UK was around 5.5% in July 2026, according to Moneyfacts. Over the past 20 years, the FTSE 100 has delivered a total annualised return, including dividends, of roughly 6.3 to 6.4%, though that figure is not guaranteed and any single year could be worse. When your mortgage rate sits close to or above what you might reasonably expect from investing, overpaying starts to look like the safer bet, because it is a guaranteed return with no volatility. When your rate is meaningfully lower, investing has historically come out ahead over the long run, but you are trading certainty for probability.

This is why so many mortgage calculators give you a different answer depending on the day you check them. The rate comparison is the right starting point, but it is not the whole picture, and most guides on this stop there.

Why pension contributions usually come first

Before you overpay anything or open an ISA, it is worth checking whether you are getting the full employer match on your workplace pension, because that is very often the best return available to you, better than either option above. Pension contributions also attract tax relief, and the annual allowance for 2026/27 is £60,000 across all sources, including your own contributions and your employer's.

This matters more than most financial content acknowledges for women specifically. According to Scottish Widows' most recent Women and Retirement report, the gender pension gap has widened to 32%, with women on track for an average retirement income of around £13,000 compared with £19,000 for men, and 29% of women not paying into a pension at all. If your pension has fallen behind, whether through career breaks, part time work, or simply not prioritising it while other costs took over, extra income is often better placed there first. A mortgage overpayment feels productive, but it does not close a pension gap.

What changes when the mortgage is joint

If you share a mortgage with a partner, this decision is rarely just about the numbers. One of you might find real comfort in watching the mortgage balance shrink, while the other would rather see that same money working harder in a pension or ISA. Neither instinct is wrong, but it helps to say it out loud rather than assume you are both optimising for the same thing. If you are the one managing the household finances, or the higher earner, it is worth being the one who starts that conversation, since the decision affects both of you even when one person is doing the sums.

A sensible order to work through

For most higher earning households, the order that makes sense is: build a cash buffer of three to six months' expenses, take the full employer pension match, clear any debt costing more than your mortgage rate, then split what is left between mortgage overpayments and a Stocks and Shares ISA based on where your mortgage rate actually sits. Most lenders allow you to overpay up to 10% of your outstanding balance each year without a penalty, so check your specific terms before committing more than that. The ISA allowance for 2026/27 remains £20,000, though from April 2027 the amount you can hold in a cash ISA specifically will be capped at £12,000 for anyone under 65, which is worth factoring in if you are currently using your ISA allowance mostly for cash.

From Lucy, co-founder of Welleness

When our mortgage deal came up for renewal a couple of years ago, I remember sitting with the numbers and feeling strangely paralysed. Not because the decision was complicated, but because I could argue either side convincingly to myself in the space of an evening. Overpay and watch the balance fall. Invest and let time do the work. Both felt sensible, which is exactly the problem.

What actually helped was talking it through with someone who wasn't emotionally attached to the outcome, who could ask me what I was actually optimising for. Was it peace of mind, was it maximising the return, was it closing a pension gap I knew I had from years of lower earning while building the business. Once I could answer that honestly, the decision made itself.

I say this because I think women in particular are quick to treat this as a maths problem to solve alone, on a Sunday evening, with a calculator and a bit of guilt about not having sorted it sooner. It is rarely just maths. It is about what you are actually trying to protect or build, and that is worth saying out loud to someone, even if the answer ends up being the sensible one you suspected all along.

What you can do now

Check your latest pension statement or log into your workplace pension portal to see whether your employer offers to match contributions above the minimum, and whether you are currently claiming the full match.

Look up your current mortgage rate and compare it honestly against a long term investment return assumption of around 6%, rather than assuming either option automatically wins.

If your mortgage is joint, set aside twenty minutes this week to ask your partner what they would actually choose with spare income, before you decide together.

Frequently asked questions

Is it better to overpay my mortgage or put money in a pension?

For most people, pension contributions come first if you are not already receiving your full employer match, because that match plus tax relief is typically a better return than either overpaying your mortgage or investing in an ISA.

How much can I overpay my mortgage without a penalty?

Most UK lenders allow overpayments of up to 10% of your outstanding mortgage balance each year without an early repayment charge, though this varies by lender and deal, so check your mortgage terms directly.

Should I overpay my mortgage before investing in a Stocks and Shares ISA?

It depends on your mortgage rate. If your rate is close to or above long term average investment returns, of around 6 to 7% based on historical UK equity performance, overpaying is the lower risk option. If your rate is meaningfully lower, investing has historically outperformed over long periods, though this is not guaranteed.

What happens to the Cash ISA allowance from 2027?

From April 2027, anyone under 65 will be able to hold up to £12,000 of their £20,000 total ISA allowance in a Cash ISA, with the remainder needing to go into a Stocks and Shares ISA or other ISA type, so it is worth reviewing how you currently split your allowance.

Here is what one Welleness member said after her financial health check helped her see the bigger picture on a decision like this one.

"Before using Welleness I thought speaking to a financial adviser was only for people who earn like 200 grand, or people who'd inherited. Without Welleness I would probably be less informed, and I wouldn't be reaching the levels of what I think I'm going to achieve now that I've spoken to Lizzie." Emily, Welleness user

If you have been going back and forth on this decision without a clear answer, our free financial health check takes less than five minutes and gives you a clear picture across six areas of your financial life, including how your pension, savings and mortgage fit together. No judgement, no jargon, just clarity on where to put your money next.

This post is for informational purposes only and does not constitute financial advice. For guidance specific to your situation, speak to a regulated financial adviser.