Buy the 5.29% Gilt, Don't Overpay the 5.63% Mortgage — Liquidity and Tax-Free Gains Beat Locked-Up Equity

Here is what the overpayment guarantee does not say. Overpaying a repayment mortgage does not lower next month's payment — it shortens the term. You still owe the same amount every month, and the bank does not refund your overpayments if you lose your job, fall ill, or need to move.

A gilt is different. You can sell it any trading day through the DMO's retail Purchase and Sale Service or a platform. The price moves, but the asset is yours to convert back into cash. Equity in a house converts back into cash only when you remortgage or sell — and both take weeks, cost money, and depend on a buyer.

Liquidity is not free, and it is not trivial. It is the difference between having a plan and having a hostage.

Gains on gilts are exempt from Capital Gains Tax under section 115 of TCGA 1992. Buy a low-coupon gilt below its £100 face value and most of your return arrives as a tax-free capital gain, not a taxable coupon. Only the coupon is income — and gilt coupon interest can sit inside your Personal Savings Allowance, which is £500 for a higher-rate taxpayer.

So the honest comparison for a 40% taxpayer is not 5.63% versus 5.29%. It is 5.63% locked in a house versus roughly 5.2% you can sell tomorrow. A fraction of a point is the entire premium for liquidity, diversification, and the right to change your mind. Our gilt-versus-cash breakdown walks through the same after-tax maths in detail.

That series ends at 4.80% in June; the September sell-off took the 10-year above 5.29%, a 19-year high. If you are buying to hold to maturity, a 19-year-high yield is not a warning — it is the price you wanted to wait for.

Strip the debate to its simplest form. £10,000 overpaid on a 5.63% mortgage saves £563 of interest this year. £10,000 in a low-coupon gilt at 5.29% earns £529 this year, nearly all of it tax-free capital gain. The difference is £34.

£34 a year. That is the entire premium the overpayment crowd asks you to pay for locking away £10,000 you cannot retrieve without selling the house or remortgaging it.

You would not pay £34 to lose access to £10,000 in any other context. A savings account that charged you £34 a year to hold your own money would be a scandal. Yet the overpayment argument wraps exactly that fee in the language of a 'guaranteed return' and calls it discipline. The mortgage hub is full of the reasoning; I am asking you to price the part it leaves out.

A fixed-rate mortgage is one of the few household liabilities that inflation quietly shrinks. You repay it in pounds that are worth less each year. Overpaying it early hands the lender today's expensive money instead of tomorrow's cheaper money.

The bond sell-off that pushed the 10-year gilt to a 19-year high is, at its core, an inflation story: oil jumped after the US and Iran exchanged fire, and investors fear higher inflation. Markets are now pricing three Bank of England hikes over the next year. If that inflation shows up, the real value of a fixed 5.63% mortgage shrinks while a paid-off mortgage leaves you holding only the memory of the money you used to clear it.

Fixed-rate debt and long-dated gilts are two sides of the same bet. You do not want to be maximally short inflation on the asset side and maximally long on the liability side. Our BoE rate-cycle explainer traces how the repricing flows through to both.

The 10-year is not the only gilt on the shelf. The BBC reports that the 30-year gilt is at its highest since 1998, while the Guardian notes that 15-year gilt yields hit 28-year highs this week — which is exactly why annuities now pay over £8,000 a year per £100,000.

A mortgage is a 20-to-30-year obligation. If your horizon matches the long end of the curve, a duration-matched gilt ladder gives you the same government credit risk as your overpayment's 'guarantee', but as an asset you can actually rebalance, gift, or sell. See our guide to buying UK gilts for the mechanics.

Concentration risk works both ways. The person who overpays the mortgage is making one enormous bet on UK residential property, funded by abandoning every other option. The investing hub makes the diversification case in full.

I will not pretend the gilt is always right. If you are within a few years of clearing the mortgage, overpay and finish it — the guarantee is worth more than a small spread when the balance is small. If you are a higher or additional-rate taxpayer with a full ISA, no emergency-fund gap, and no other use for the cash, a 5.63% tax-free return on overpayment is a perfectly good outcome, as the overpay-the-mortgage case argues.

But that is a narrow case. The average borrower in 2026 has a 5.59% two-year fix, a stretched budget, and — if the oil-driven inflation story plays out — a reason to keep money where they can reach it. For that borrower, the gilts hub answer is the liquid one: buy the low-coupon gilt, keep the optionality, and let inflation do the heavy lifting on the debt.