Mortgages Pensions Investing
10 minute read · Updated February 2026
My brother-in-law called me last year, £400 burning a hole in his pocket every month after his kids started school and childcare costs dropped off. His mortgage was at 4.7%. He had a workplace pension he'd barely touched. He wanted a definitive answer.
I couldn't give him one — not without asking about six more things first. But by the end of that conversation, the right answer for him was clear. And it probably is for you too, once you know what to look for.
This is the framework I walked him through. No waffle, no "it depends" without explanation. Just the actual decision tree, with real numbers.
Before anything else: does your employer match your pension contributions?
If the answer is yes and you're not contributing enough to get the full match, stop reading this article and go fix that right now. I mean it. Come back afterwards.
Here is why it is that important. Say you earn £48,000 and your employer matches up to 5% of salary. That is £2,400 a year of free money sitting on the table. If you are putting in 2% and they are matching 2%, you are leaving £1,440 of your employer's contributions behind — every single year — in order to pay down a 4.7% mortgage fractionally faster. The maths on that is not close. The employer match wins by a landslide.
The reason so many people miss this is that the match is invisible. It does not show up as a salary increase. It does not appear in your bank account. It is silently piling up (or not) in a pension you rarely look at. But it is the most powerful wealth-building mechanism most employed people have access to, and it requires no investment skill whatsoever — just showing up with enough of your own contribution to unlock it.
So: employer match fully captured? Good. Now we can talk about what to do with the rest.
Overpaying your mortgage gives you a guaranteed return equal to your interest rate. If your rate is 4.7%, every pound you overpay saves you 4.7% per year with zero risk, zero tax, and complete certainty. You cannot lose money doing this.
Investing — in a pension, ISA, or LISA — offers higher potential returns but with uncertainty attached. A globally diversified index fund has returned roughly 7–9% annually over long periods. But markets do go down. 2022 was not fun. And you will not know for decades whether any given year's contributions grew as expected.
So the naive version of the question is: is a guaranteed 4.7% better than an uncertain 7–9%? And the honest answer is that for most people in most circumstances, the uncertainty is worth accepting — because of what tax relief does to the effective maths.
This is where a lot of people's mental model breaks down, because pension contributions do not work like putting money in a savings account. When you contribute to a pension, the government adds money on top.
If you pay basic rate tax (20%), a £100 pension contribution costs you £80 out of your take-home pay. HMRC quietly adds the other £20 back in. If you pay higher rate tax (40%), that same £100 into your pension costs you just £60 — and if you are using salary sacrifice, you save National Insurance on top of that, bringing the effective cost down further.
Let me make this concrete. Priya is 36, earns £52,000, and pays 40% tax on her income above £50,270. She wants to put £400 a month somewhere sensible.
That is an 85% instant return on her out-of-pocket cost. No mortgage rate comes close.
For basic rate taxpayers the maths is less dramatic but still compelling. Marcus is 29, earns £34,500, and wants to put £300 a month to work. Via salary sacrifice his actual monthly cost is around £234. £300 goes into his pension. His effective "instant return" is around 28% — still well ahead of a 4.7% mortgage saving.
All that said, there are genuine situations where the mortgage wins. Here they are:
This is the scenario where overpaying is most defensible. At 5.5% or 6%, the guaranteed saving is substantial and hard to beat once you strip out the pension tax advantages that do not apply if there is no employer match and you are not a higher rate taxpayer. The ISA offers no upfront tax relief, so a 5.5% guaranteed saving can genuinely compete with an expected 7% market return once you account for the risk.
Tom is 58. He has £34,000 left on his mortgage at 5.1% and five years remaining. Overpaying aggressively right now could clear it in two to three years. Once it is gone, that £800-a-month payment gets redirected into his pension at a time when it has exactly the runway it needs to grow before he retires. Clearing the mortgage first to unlock that cash flow makes complete sense here.
This is not a cop-out answer — it is real. If carrying debt causes you actual anxiety, the psychological return from reducing it is legitimate. You will sleep better, make better decisions in other areas of your life, and stick to the plan more consistently. A mathematically slightly suboptimal strategy you actually stick to beats a theoretically optimal one you abandon or resent.
If you earn well and have been contributing seriously for years, you might be approaching the £60,000 annual pension allowance. Once you are there, the ISA is next, and if you have maxed the ISA too, mortgage overpayment becomes the logical home for spare cash.
Assume you have £400/month to put somewhere. 25-year time horizon. Mortgage rate 4.7%.
| Option | Your monthly cost | What goes to work | Effective starting position |
|---|---|---|---|
| Mortgage overpayment | £400 | £400 off balance | 4.7% guaranteed saving |
| Pension — basic rate taxpayer | ~£320 (via salary sacrifice) | £400 into pot | 25% up before any growth |
| Pension — higher rate taxpayer | ~£216 (via salary sacrifice) | £400 into pot | 85% up before any growth |
| Pension + 5% employer match (£48k salary) | ~£320 | £800 into pot | 150% up before any growth |
| Stocks & Shares ISA | £400 | £400 invested | 0% boost — relies entirely on growth |
Salary sacrifice NI saving assumes earnings between £12,570 and £50,270. Higher rate assumes income above £50,270.
If you are trying to figure out what to do with spare money each month, here is the sequence I would work through:
The Stocks & Shares ISA sits in an interesting middle ground. There is no upfront tax relief — you invest from take-home pay — but all growth and income is tax-free, and crucially you can access the money any time without penalty. That flexibility has real value, particularly if you want to build wealth you might need before retirement age.
The Lifetime ISA is worth a separate mention if you are under 40. The government adds 25% to everything you contribute — up to £1,000 free money per year on a £4,000 contribution. For a basic rate taxpayer, that is comparable to pension tax relief. The catches are the £450,000 property limit for first-time buyers and a 25% withdrawal penalty if you access the money for anything other than a first home purchase or retirement from age 60.
For most employed UK homeowners: capture your employer match first, always. Then, if you are a higher or additional rate taxpayer, more pension contributions are almost certainly better than overpaying the mortgage at current rates. If you are a basic rate taxpayer with no employer match and a mortgage above 5%, overpaying is a very respectable choice. The ISA adds flexibility alongside either. The exact right answer depends on your specific numbers — which is what the calculator is for.
Plug in your salary, mortgage rate, employer match and tax band. The calculator shows all four options side by side with projected outcomes — takes about 30 seconds.
Try the free calculator →