Should I overpay my mortgage or invest?
How to weigh a guaranteed saving on mortgage interest against the potential, but uncertain, growth from investing, with a worked example.
By Asis Tewari Published · Last reviewed · 4 min read
The short answer
It depends on your mortgage rate, how long you can leave money invested, how much risk you are comfortable with and whether you might need the money before your mortgage ends. Overpaying gives a guaranteed saving on interest but ties money up in your home. Investing offers the potential for growth and may keep your money easier to reach, but its value can fall and you may get back less than you put in.
Key takeaways
- Overpaying is a guaranteed saving on interest, for as long as your rate applies.
- Investing may grow more over the long term, but it can fall in value. Capital at risk.
- Money paid into your home is hard to get back out. Money invested is usually easier to reach.
- Many homeowners do a bit of both.
What does overpaying your mortgage actually do?
When you overpay, you pay more than your required monthly payment. The extra reduces the amount you owe, so you pay less interest from then on. Depending on how your lender applies it, you either finish your mortgage sooner or your future monthly payments go down.
The saving is guaranteed. If your mortgage rate is 4.5%, every £1 you overpay saves interest at 4.5% a year for as long as that rate applies.
What does investing the same money do?
If you invest the same amount each month, for example in a low-cost index fund held in a Stocks and Shares ISA, your money is exposed to the stock market. Over long periods, investing may offer the potential for higher returns than your mortgage rate. Over shorter periods, values can fall, and there is no guarantee of any return.
Overpaying vs investing, side by side
| Overpay your mortgage | Invest in an index fund | |
|---|---|---|
| Return | Guaranteed saving equal to your mortgage rate | Not guaranteed. Can go down as well as up |
| Access to your money | Usually locked into your home | Investments can usually be sold, although their value may be lower than you paid |
| Tax | No tax on interest saved | Tax-free inside an ISA. May be taxable in a General Investment Account |
| Effect at remortgage | A lower balance can move you into a lower loan-to-value band | No direct effect on your mortgage |
Questions to ask yourself first
Before choosing either option, guidance from MoneyHelper suggests checking a few things:
- Do you have an emergency fund? Keeping some cash you can reach quickly matters before you lock money into your home or the stock market.
- Do you have more expensive debts? Credit cards and personal loans usually charge much more than a mortgage.
- Are you making the most of your pension? Pension contributions can benefit from tax relief and employer contributions.
- How long can you leave the money alone? Investing is generally more suitable for money you won't need for at least five years.
- What does your mortgage allow? Many lenders let you overpay up to 10% of your balance a year without a charge, but limits vary. See how much you can overpay without a penalty.
A worked example
Take an illustrative mortgage of £300,000 at 4.5% with 22 years left, and £400 a month of spare money. These figures come from the nume calculator and assume the interest rate stays the same for the whole term:
- Overpaying £400 a month could clear the mortgage about 5 years and 11 months early and save around £52,000 in interest. This saving is guaranteed if the rate stays the same.
- Investing £400 a month instead, with an assumed return of 5% a year after nume's 0.40% platform fee, could build a pot large enough to clear the remaining balance about 6 years early. At an assumed 3% a year, that falls to about 5 years and 3 months; at 7%, it rises to about 6 years and 9 months.
At these numbers, the two options finish within a few months of each other, but only one of them is guaranteed. If returns are lower than assumed, investing could leave you worse off than overpaying. This example ignores tax, fund management fees and early repayment charges.
So which is right for you?
There is no single answer. Overpaying can suit you if your mortgage rate is high, you value certainty, or you want to reduce your loan-to-value before remortgaging. Investing can suit you if you can leave money invested for the long term, you are comfortable with the value going down as well as up, and you want to keep more of your wealth outside your home. Many homeowners do a mix of both.
nume shows you both options with your own numbers. It does not give personal advice. If you're unsure, consider speaking to a regulated financial adviser.
FAQs
Can I overpay and invest at the same time?
It can be possible to do both, depending on your circumstances and mortgage terms. Some homeowners split their spare cash, for example overpaying enough to reach a lower loan-to-value band at their next remortgage and investing the rest. Capital is at risk on investments.
Is money I overpay into my mortgage easy to get back?
Usually not. Once you overpay, the money becomes part of the equity in your home. Some flexible or offset mortgages let you draw overpayments back, so check your mortgage terms.
Do I pay tax on the interest I save by overpaying?
No. A saving on mortgage interest is not taxed. Investment growth may be taxed unless it is held in a tax wrapper such as a Stocks and Shares ISA. Tax treatment depends on your individual circumstances and may change.
Sources
- MoneyHelper: Should you pay off your mortgage early? (accessed 3 October 2026)
- GOV.UK: Individual Savings Accounts (ISAs) (accessed 3 October 2026)
Mortgage decisions, made clearer
Get occasional insights on overpayments, investing and fixed-rate changes, without the jargon.
This guide is for information only and is not personal advice. Tax treatment depends on your individual circumstances and may change. If you invest, your capital is at risk. The value of investments can go down as well as up, and you may get back less than you invest. Your home may be repossessed if you do not keep up repayments on your mortgage.