Calculators Hub
Explore tools to plan and compare
A growing collection of quick, no-login calculators to help you weigh up mortgage overpayments, investing, budgeting, and long-term planning. All run in your browser.
Mortgage vs investing UK
Mortgage Overpayment vs. Investing Calculator (UK)
Should You Pay Off Your Mortgage Early or Invest in the Stock Market?
Deciding whether to clear your home loan or grow an investment portfolio is one of the most debated topics in UK personal finance. This calculator helps you compare the guaranteed saving of mortgage interest against the potential growth of an investment like a Stocks and Shares ISA or a low-cost index fund.
In one sentence
You enter your mortgage details and a monthly amount. We compare two choices: overpaying the mortgage vs investing the same amount.
What this helps with
- • If you have extra money each month and want to choose where it goes.
- • To understand the trade-off between a “guaranteed saving” (mortgage interest) and “possible growth” (investing).
- • To get a quick estimate — not a perfect prediction.
Examples to try
Tap a button to auto-fill the form with simple UK-style numbers.
Results
Quick result (easy summary)
These are rough estimates (they don't include inflation or fees).
Mortgage interest you might avoid
£36,280
This is the interest you may not pay if you overpay each month.
Your investment pot could grow to
£162,959
This is what your invested money might be worth after 25 years.
Extra money you might have by investing
£126,679
Compared to overpaying your mortgage.
Mortgage paid off by overpaying
Feb 2045
Without overpaying, the mortgage would finish around Mar 2051.
That clears the mortgage 6 years 1 month earlier.
The "same result" mortgage rate
11.95%
At about this mortgage rate, both choices come out similar (based on your assumptions).
If your actual mortgage rate is higher than this, overpaying tends to look better. If lower, investing tends to look better.
Simple takeaway
If you invest the extra money instead of overpaying your mortgage, you could end up with about £126,679 more after 25 years.
Mortgage balance vs portfolio growth
This shows how the invested pot and remaining overpaid mortgage balance could change year by year.
Year 25
How to read the results
- • Mortgage interest saved shows how much interest you might avoid paying by overpaying.
- • Investment value shows what the invested money could grow to, using your return guess.
- • Break-even mortgage rate is the rate where both options come out roughly the same.
How it works
- 1) We use your mortgage rate to see how much interest overpayments could save.
- 2) We grow the same monthly amount in an ISA, pension, or taxable account using your return guess.
- 3) We show the difference so you can see which path might leave you ahead.
Your inputs stay in your browser. These are simple estimates — real life can vary.
Yearly breakdown
Shows the end-of-year totals so they align with the summary figures above.
| Year | Interest saved (cum) | Investment balance | Difference |
|---|---|---|---|
| Year 1 | £50 | £2,493 | £2,443 |
| Year 2 | £213 | £5,166 | £4,953 |
| Year 3 | £493 | £8,033 | £7,539 |
| Year 4 | £897 | £11,106 | £10,209 |
| Year 5 | £1,429 | £14,402 | £12,973 |
| Year 6 | £2,096 | £17,936 | £15,840 |
| Year 7 | £2,904 | £21,726 | £18,822 |
| Year 8 | £3,859 | £25,789 | £21,930 |
| Year 9 | £4,969 | £30,147 | £25,178 |
| Year 10 | £6,240 | £34,819 | £28,579 |
| Year 11 | £7,679 | £39,829 | £32,150 |
| Year 12 | £9,295 | £45,201 | £35,906 |
| Year 13 | £11,095 | £50,962 | £39,867 |
| Year 14 | £13,088 | £57,139 | £44,051 |
| Year 15 | £15,283 | £63,762 | £48,479 |
| Year 16 | £17,689 | £70,865 | £53,176 |
| Year 17 | £20,316 | £78,480 | £58,165 |
| Year 18 | £23,174 | £86,647 | £63,473 |
| Year 19 | £26,271 | £95,403 | £69,132 |
| Year 20 | £29,210 | £104,793 | £75,584 |
| Year 21 | £31,670 | £114,862 | £83,191 |
| Year 22 | £33,631 | £125,658 | £92,027 |
| Year 23 | £35,069 | £137,235 | £102,165 |
| Year 24 | £35,961 | £149,648 | £113,688 |
| Year 25 | £36,280 | £162,959 | £126,679 |
Example scenario
Example scenario
If you want a simple side-by-side example, here is a common mortgage versus investing scenario.
- Mortgage balance: £200,000
- Mortgage rate: 4.5% with 25 years left
- Monthly overpayment or investment: £200
- Expected investment return: 7% a year
This gives you a quick way to compare a known mortgage interest saving against a more uncertain investment return over the same time period.
Learn the basics
How the Mortgage Overpayment vs. Investing Calculator (UK) Works
How to Decide: The "Interest Rate vs. Growth" Rule
The Interest Rate Baseline: Paying off your mortgage is effectively a "guaranteed return" equal to your mortgage interest rate. If your rate is 5%, every £1 overpaid saves you 5% in interest costs.
The Investment Hurdle: For investing to be mathematically superior, your after-tax returns must beat your mortgage rate. Historically, broad stock market indexes such as the S&P 500 or FTSE World Index have averaged around 7% to 10% annually over long periods, but this is never guaranteed.
Tax Efficiency: Remember that investing inside an ISA or SIPP can protect your gains from tax, whereas overpaying a mortgage uses post-tax income but simplifies your long-term liabilities.
Pros vs cons
Pros
- Useful for comparing mortgage overpayments with long-term investing in one place.
- Shows the opportunity cost of choosing debt reduction over portfolio growth.
- Works well for UK users comparing mortgage rates with ISA or pension-style returns.
Cons
- Future market returns can be lower or higher than the rate you assume.
- Mortgage rates, fees, and tax rules can change after you run the comparison.
- The maths cannot fully capture risk tolerance or the emotional value of becoming debt free.
Glossary
- Amortisation
- The process of paying down a loan over time through regular payments that cover both interest and principal.
- Opportunity cost
- What you miss out on by choosing one financial option instead of another.
Frequently asked questions
Is it better to overpay my mortgage or invest in 2026?+
It depends heavily on your mortgage rate. If your rate is around 4.5% to 5.5%, the gap between a guaranteed mortgage saving and possible long-term stock market growth is much smaller than it was when mortgage rates were very low.
Are there penalties for overpaying my mortgage?+
Many UK lenders allow overpayments of up to 10% of the balance each year without an early repayment charge, but you should always check your own mortgage terms before making large overpayments.
What is the opportunity cost of overpaying?+
It is the potential investment growth you miss by choosing the safer route of debt reduction instead of putting that money into the market.
Related calculators
Try the next step after Mortgage Overpay vs Invest
These tools answer nearby questions, so you can compare the next trade-off without starting from scratch.
Mortgage
Lump Sum: Overpay vs Invest
Test whether a lump sum is more useful reducing your mortgage or aiming for investment growth.
Open calculatorRetirement
Mortgage Overpay vs Pension
See whether spare monthly cash is more useful in your pension or on your mortgage.
Open calculatorMortgage
Mortgage Payment Calculator
Estimate your monthly mortgage payment and the total cost of borrowing.
Open calculatorThese calculators are for educational purposes only and do not constitute financial advice.
They use simplified assumptions and browser-based estimates. Read the full disclaimer before making important decisions.