Should I Overpay My Mortgage or Invest?

Overpaying your mortgage gives you a guaranteed return equal to your mortgage rate. Investing gives you a potentially higher return with no guarantees. In June 2026, with five-year fixed rates averaging around 5.5%, the two paths are closer than they have been in years.

Last updated: 21 June 2026

The guaranteed return you already have

Every pound you pay off your mortgage saves you interest at your current mortgage rate. That saving is guaranteed, immediate, and risk-free. No market can take it away.

On a 5.5% mortgage, overpaying £200 a month is the financial equivalent of earning 5.5% a year on that money with certainty. A savings account paying 5.5% would be exceptional. A guaranteed investment return of 5.5% does not exist.

The case for investing rests on equities delivering higher average returns over time. Historically they have: global developed-market equities have returned roughly 7–9% per year in nominal terms over multi-decade periods. But that is an average across volatile years. The FTSE All-World was down 20% in 2022 and up 25% in 2023. If your mortgage rate is low enough, the average equity return clears it comfortably. At current rates around 5.5%, the margin is thin.

The break-even test

The comparison comes down to one question: can your investments reliably beat your mortgage rate after tax? The table below shows how the case shifts at different rates.

Mortgage rate	Guaranteed return from overpaying	Verdict
3.0%	3.0%	Investing likely wins over 10+ years
4.0%	4.0%	Investing edge, but smaller margin
4.5–5.0%	4.5–5.0%	Close call; depends on risk appetite and time horizon
5.5%	5.5%	Overpaying is competitive on a risk-adjusted basis
6.5%+	6.5%+	Overpaying is very hard to beat reliably

Verdicts based on long-term equity return averages. Your individual rate, remaining term, and tax situation all affect the outcome.

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Mortgage Repayment Calculator

Enter your balance, rate, and a monthly overpayment amount. See how many years you'd cut off your term and how much interest you'd save.

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Why the ISA changes the comparison

Outside an ISA, investment returns are eroded by tax. Capital gains (the profit when you sell) above the £3,000 annual CGT exemption face Capital Gains Tax at 18% for basic-rate taxpayers or 24% for higher-rate taxpayers in 2026/27. Dividend income above the £500 allowance is taxed at 8.75% (basic rate) or 33.75% (higher rate).

Inside a stocks and shares ISA, all growth and income are completely tax-free, year after year. A 7% gross return stays a 7% net return. For a higher-rate taxpayer investing in a general account, the same 7% fund return could net closer to 5% or 5.5% once CGT on disposal is accounted for.

The practical rule: if you have unused ISA allowance (£20,000 for 2026/27), use it for investments before comparing to mortgage overpayment. You are otherwise comparing a taxable investment return against a guaranteed, tax-free saving on your mortgage. They are not equivalent.

The Scottish angle

CGT and dividend tax are UK-wide, so Scottish taxpayers face the same investment tax rates as English ones. The difference is Scotland's lower higher-rate threshold: £43,663 in 2026/27, compared to £50,270 in England and Wales. More Scottish earners are classified as higher-rate taxpayers, which increases the tax cost of holding investments outside an ISA. If you earn above £43,663 in Scotland, the case for filling your ISA allowance before any general account investing is marginally stronger.

A worked example at current rates

Sarah has £200,000 left on her mortgage at 5.5%, with 22 years remaining. She can afford £300 a month more than her minimum payment. Here are both paths.

Path A: Overpay the mortgage by £300 a month

Overpaying by £300 a month cuts the remaining term from 22 years to roughly 17 years and saves approximately £37,000 in interest. Each £300 earns a guaranteed 5.5% return. Once the mortgage is gone, her monthly cashflow increases permanently by the full repayment amount for the remaining years.

Path B: Invest £300 a month in a stocks and shares ISA

Investing £300 a month for 22 years at 7% annual return produces approximately £185,000 in nominal terms. At 5% annual return, the figure is around £145,000. The investment pot grows alongside the mortgage: she still owes the balance and still pays interest throughout.

At 7% returns, the investment pot outgrows the interest saved on paper. But that 7% is an assumption, not a contract. In years where markets fall sharply, the comparison flips hard, and the mortgage is still there.

To model the investment side for your own numbers, the Compound Interest Calculator shows what a regular monthly contribution becomes at different return rates over time.

	Path A: Overpay	Path B: Invest at 7%	Path B: Invest at 5%
Monthly extra cash	£300	£300	£300
Time horizon	22 years	22 years	22 years
Outcome	£37,000 interest saved, mortgage cleared 5 years early	~£185,000 investment pot	~£145,000 investment pot
Risk	None — guaranteed	Market volatility	Market volatility
Liquidity	Illiquid (locked in property)	Accessible within days	Accessible within days

Example: £200,000 mortgage, 5.5% rate, 22 years remaining. Investment figures are nominal. Approximate 2026 figures — use the calculators for your exact numbers.

What the rate comparison misses

The maths treats the two options as equivalent except for return rates. They are not.

Overpayment limits on fixed-rate deals

Most fixed-rate mortgages allow overpayments of up to 10% of the outstanding balance per year without an early repayment charge (ERC). Overpaying beyond that triggers the ERC, which can be several per cent of the balance. Check your mortgage terms before committing to a regular overpayment level. Within the 10% limit, the process is penalty-free.

Liquidity

Money paid into a mortgage is illiquid. You cannot get it back without remortgaging or selling the property. Money in a stocks and shares ISA is accessible within days. If your income is variable or your emergency fund is thin, the liquidity of the ISA has practical value that a return comparison cannot quantify.

Loan-to-value and your next remortgage

Reducing your mortgage balance improves your loan-to-value (LTV) ratio, the proportion of the property's value you owe. A lower LTV unlocks better rates when your current fixed deal ends. If you are close to an LTV threshold (such as 75% or 60%), targeted overpayment before your next remortgage date can produce a meaningful saving on future rates.

Time horizon

Over 5 years, global equity markets could be anywhere. Over 20 years, the range of outcomes is much narrower and has historically always been positive in developed markets. If your mortgage has fewer than 7 years left, the short time horizon reduces the case for investing over overpaying considerably.

A practical order of priority

For most people in 2026, this ordering makes sense before the overpay-vs-invest question even arises:

1 Emergency fund. Three to six months of expenses in accessible savings. Overpaying a mortgage with no cash buffer is the wrong sequence.
2 Workplace pension to the employer match. If your employer matches contributions, that is an immediate 50–100% return on the matched portion. Take the full match before directing cash elsewhere.
3 ISA allowance. Up to £20,000 in 2026/27 sheltered from all future CGT and dividend tax. Filling available ISA room before investing in a general account changes the comparison materially.
4 Overpay or invest further. Once the ISA is used, compare your mortgage rate against your expected net return from a general account. At current rates around 5.5%, either choice is defensible. Splitting the spare cash between both is a valid middle path.

If your salary is near £100,000, pension contributions become far more efficient than either option because of the 60% effective marginal rate on income between £100,000 and £125,140. The 60% tax trap guide covers that case in detail. Scottish earners in the same range face 67.5%.

To run the overpayment numbers for your own mortgage, the Mortgage Repayment Calculator shows your interest saving and term reduction at any overpayment level.

Frequently asked questions

Should I pay off my mortgage or invest?

The maths favours investing if your expected after-tax return exceeds your mortgage rate, and overpaying if your rate is higher. In June 2026, with five-year fixes averaging around 5.5%, the two paths are very close. For most people the practical answer is: fill your ISA first, then direct what remains to whichever option your rate makes more attractive.

What is the break-even mortgage rate between overpaying and investing?

There is no single break-even rate because investment returns are not guaranteed. As a rough guide: below 4%, long-term equity investing has historically outpaced the guaranteed saving from overpaying. Above 5.5%, the guaranteed return from overpaying starts to compete seriously with equities on a risk-adjusted basis. At current rates around 5.5%, overpaying is a defensible choice even if equities average slightly higher.

Does it matter whether I invest inside or outside an ISA?

Yes. Outside an ISA, investment gains face Capital Gains Tax (18% at basic rate, 24% at higher rate for 2026/27) and dividends above the £500 allowance are taxable. Inside a stocks and shares ISA, all growth and income are completely tax-free. If you have unused ISA allowance, fill it before comparing a taxable investment account against overpaying your mortgage.

Does this work differently in Scotland?

CGT and dividend tax are UK-wide, so the tax treatment of investments is the same in Scotland as in England. The difference is Scotland's lower higher-rate threshold: £43,663 in 2026/27 versus £50,270 in rUK. More Scottish earners fall into the higher rate, which increases the cost of holding investments outside an ISA. The case for using your ISA allowance first is marginally stronger in Scotland as a result.

What about the peace of mind from owning your home outright?

The guaranteed, risk-free nature of overpaying has real value beyond the maths. Owning your home outright removes the risk of losing it if your income falls, reduces your fixed monthly costs permanently, and improves your loan-to-value ratio for future remortgaging. None of this shows up in a rate comparison.

Should I build an emergency fund before overpaying?

Yes. Three to six months of expenses in accessible savings should come before either overpaying or investing. Money paid into a mortgage is illiquid: you cannot get it back without remortgaging. If you face a sudden income drop, an overpaid mortgage offers no protection the way a cash buffer does.