25-year full-life fix mortgages: the amortisation maths (UK, 2026)
The Bank of England's most recently published quoted rate for a 75% loan-to-value 5-year fixed mortgage stands at 4.32% as of April 2026 (Bank of England, Quoted Household Interest Rates, retrieved 8 June 2026). A new class of UK product — Habito One, April Mortgages, Perenna — fixes a single rate for the entire 25-year term, removing the conventional reset at year 5. Quoted long-fix rates from these lenders typically sit 50 to 100 basis points above the BoE 5-year average.
This piece walks the amortisation on a single £270,000 loan (£300,000 purchase, 10% deposit, 25-year capital repayment) at three rates: 4.32%, 4.82% and 5.32%. No forecasts, no recommendations — just what the payment schedules say.
The headline numbers
| Product | Quoted rate | Monthly payment | Lifetime interest (25 years) |
|---|---|---|---|
| BoE 75LTV 5-year fix (most-recent print) | 4.32% | £1,473.30 | £171,989 |
| 25-year full-life fix at +50 bps | 4.82% | £1,550.21 | £195,062 |
| 25-year full-life fix at +100 bps | 5.32% | £1,629.14 | £218,742 |
Numbers assume the same rate runs unbroken for the whole 25 years. That assumption is realistic for the full-life-fix products by definition; for the 5-year fix it is counterfactual — a flat-rate scenario used only to size the premium. The real-world 5-year-fix path resets every five years to whatever is available at the time.
The premium for permanent rate certainty:
- +50 bps premium: an extra £76.91 per month, or £23,073 of additional interest across 25 years.
- +100 bps premium: an extra £155.84 per month, or £46,753 of additional interest across 25 years.
What you're actually buying
A 25-year full-life fix collapses every future remortgage decision into the present one. There is no reset at year 5. There is no stress test for the next product. The borrower's monthly figure on day one is the borrower's monthly figure in month 300. From a household-cashflow perspective, the mortgage payment behaves like the council tax bill — a known number running on a known clock.
That structural difference matters for three reasons.
Affordability is assessed once. Under the FCA's Mortgage Conduct of Business rulebook (MCOB 11.6), lenders must satisfy themselves that a borrower can afford the payment over the term — but the affordability test runs against the agreed product. When the product is fixed for the term, the test is fixed for the term. There is no second assessment at year 5 if the borrower's income has fallen or their dependants have grown.
Equity build is the same. A 25-year full-life fix at 5.32% builds capital on exactly the same amortisation curve as a 25-year capital-repayment mortgage at 5.32% on any other product structure. The borrower owns the same equity share at any given month. The premium buys rate insurance, not faster ownership.
Early repayment charges sit across the whole term. This is the trade-off the press tends to under-flag. A 5-year fix carries ERCs only inside its initial 5-year window; outside that window, the borrower can remortgage, overpay, or move freely. A 25-year full-life fix typically carries ERCs across a much longer window — though Perenna, for example, publicly markets a 5-year-only ERC structure on a 30-year fix, and the precise schedule varies by lender. See our companion piece on ERC constraints in falling-rate environments for the mechanics.
The rate-shock break-even
The clean way to think about the premium is to ask: at what year-5 remortgage rate does the conventional 5-year-fix-and-roll path cost the same as the full-life fix?
Starting balance: £270,000 at 4.32% for years 0–5, leaving £236,494 outstanding at year 5 (capital repayment, 25-year schedule). The borrower then remortgages the residual onto a 20-year term at whatever rate is available.
| Year-5 reset rate | Monthly post-reset | 25-year total cost | vs 25-y fix @ 4.82% | vs 25-y fix @ 5.32% |
|---|---|---|---|---|
| 3.32% | £1,349.80 | £412,349 | –£52,714 | –£76,393 |
| 4.32% (flat) | £1,473.30 | £441,989 | –£23,073 | –£46,753 |
| 5.07% (break-even vs 4.82%) | £1,565.05 | £465,062 | £0 | –£23,680 |
| 5.32% | £1,602.86 | £473,085 | +£8,022 | –£15,657 |
| 5.81% (break-even vs 5.32%) | £1,668.10 | £488,742 | +£23,680 | £0 |
| 6.32% | £1,738.26 | £505,581 | +£40,518 | +£16,839 |
| 7.32% | £1,879.23 | £539,414 | +£74,352 | +£50,672 |
Reading this row by row: the 5-year-fix-and-roll path comes out ahead if rates at year-5 reset are 5.07% or lower (vs the +50 bps full-life fix), or 5.81% or lower (vs the +100 bps full-life fix). Above those thresholds, the full-life fix wins.
Whether 5.07% or 5.81% is a likely year-5 quoted rate is not a question this article will answer. The BoE 75LTV 5-year series sat at 4.32% in April 2026, with monthly prints over the prior twelve months ranging 4.32% to 4.62%. The same series printed above 5% in 2023. The Bank of England does not publish forecasts of household mortgage rates, and neither does Homecost.
The product landscape
Three UK lenders are commonly cited as offering full-life or near-full-life fixed-rate mortgages in 2026:
- Habito One — fixed terms typically advertised from 10 to 40 years.
- April Mortgages — UK 15-year fixed-rate product.
- Perenna — long-term fixed-rate mortgages, with 20- to 30-year fixes.
This list names the participants only as illustrations of the structural product type. Quoted rates, fees, eligibility criteria, ERC schedules and overpayment allowances vary significantly between lenders and shift monthly. A live broker quote — or each lender's own published product information — is the authoritative source for any specific calculation.
The Bank of England's Financial Stability Report has acknowledged that long-duration fixed-rate mortgages currently make up a small share of UK new lending, in contrast to markets such as Denmark and the United States. Whether that share grows is a market question and not one Homecost takes a view on.
Worked example: the comparator
The same £300,000 / 10% deposit / 25-year scenario is loaded directly into the on-site mortgage comparison calculator. Run two products side by side — one at 4.32% over 25 years, one at 5.32% over 25 years — and the monthly and lifetime delta surfaces immediately. The tool also lets you flex the term, deposit and overpayment fields, so the same exercise scales to a £200,000 purchase or a £500,000 purchase without retyping the maths.
Borrowers comparing the certainty-vs-flexibility trade-off may also find the rate stress test for buy-vs-rent breakeven useful — that piece runs the same £300k baseline against the rental alternative under different rate shocks. The 25-vs-35-year term-extension trap explainer covers the second-order consequence of stretching the term to reduce the monthly. And Cost Intelligence lists the rest of the worked-example series.
What this article does not say
It does not say a 25-year full-life fix is the right product, the wrong product, or the product for any specific borrower. It does not forecast where 5-year mortgage rates will sit in April 2031. It does not value any individual property. It does not compare specific lenders on a commercial basis.
It says that, on the published BoE quoted rate and on plausible long-fix premiums of 50 to 100 basis points, the cashflow signature of the full-life fix is £77 to £156 of additional monthly payment, and the rate-stress break-even at year-5 reset is 5.07% or 5.81% depending on the premium chosen.
The right product for any given borrower depends on factors this article cannot see: term-length plans, expected income trajectory, household composition, attitude to remortgage admin, deposit size, lender appetite and a hundred other variables.
Based on 848,775 Land Registry transactions completed in calendar 2025, of which 59,438 fell in the £285,000–£315,000 band around the £300,000 baseline used here, the worked example sits in a part of the price distribution where this product class is actively considered by typical mainstream borrowers. See the full /blog for the rest of the worked-example library.
This is general information about mortgage product mechanics, not financial advice. Speak to a qualified mortgage adviser before acting.