Rate stress test: what happens to buy-vs-rent breakeven if remortgage rates change
A 5-year fix is a five-year shield. The bigger question for buyers in 2026 is what happens at year six, when the rate locked at the April 2026 Bank of England quoted rate of 4.32% expires and a new one has to be agreed at whatever the market is offering. This piece runs the same buy-vs-rent breakeven model used elsewhere in our Cost Intelligence guides against five rate-reset scenarios: −1pp, flat, +1pp, +2pp and +3pp on the year-six remortgage.
The headline finding is counterintuitive and worth stating up front. Across every reset scenario tested — including a +3pp shock back to roughly the post-mini-budget 2022 range — a buyer at today's rates still lands ahead of a renter on cumulative cash cost by year 15. The horizon for that breakeven barely shifts. What the rate shock actually changes is the total interest bill across the life of the mortgage, where the gap between the best- and worst-case scenarios runs to £127,000.
The scenario being stress-tested
The baseline matches the worked example in our parent piece on buying vs renting in the UK:
- Home price: £300,000
- Deposit / LTV: 10% deposit, 90% LTV, £270,000 loan
- Year 1-5 rate: 4.32% (BoE 75% LTV 5-year fix quoted rate, April 2026)
- Term: 25 years, capital-and-interest repayment
- Rent comparison: £1,200 per month, 3% annual increases
- Buyer's year-one sunk costs: £4,000 (conveyancing, survey, mortgage fee, removals, year-one insurance — see Hidden costs of buying a house)
- Sale-side cost (when buyer eventually sells): £6,000 (typical 2% agent + conveyancing on a £300,000 sale)
Year-one monthly payment at 4.32% over 25 years on the £270,000 loan is £1,473. That number is locked for five years.
What happens at month 61 — when the fix expires — is the part that buyers cannot price today, because nobody knows where rates will be in 2031. So instead of guessing, the standard practice is to stress-test: run the same scenario at several reset rates and see how the answer changes.
The five reset scenarios
The five scenarios bracket a wide range of remortgage outcomes against today's 4.32% starting rate.
| Reset scenario | New rate at year 6 | Year 6-25 monthly payment | Change vs year-5 payment |
|---|---|---|---|
| −1pp (rate-cut cycle) | 3.32% | £1,350 | −£124 |
| Flat (no change) | 4.32% | £1,473 | £0 |
| +1pp | 5.32% | £1,603 | +£130 |
| +2pp | 6.32% | £1,738 | +£265 |
| +3pp (shock) | 7.32% | £1,879 | +£406 |
Computed against the residual loan balance after 60 monthly payments at 4.32% (around £237,500), with the remaining 20-year term re-amortised at the new rate. The £406-a-month gap between a −1pp cut and a +3pp shock is the part of the monthly cost that is genuinely unknowable five years out.
For a longer historical anchor, the Bank of England's Bankstats series for the 75% LTV 5-year fixed quoted rate has moved by several percentage points within multi-year windows since the series began. A +1pp swing within a 12-month window has been observed more than once in the last decade, and the post-mini-budget period in late 2022 saw the series move sharply within months. Without forecasting where rates will land at any specific future remortgage date, a stress test that covers ±3pp around today's rate sits inside the published historical range.
Cumulative cash cost: buy vs rent, year by year
The cumulative-cost table is the heart of the analysis. It compares total cash paid by the buyer (year-one sunk costs plus cumulative mortgage interest — equity built is not a cost, so it is excluded) against total cash paid by the renter (cumulative rent at £1,200/month escalating at 3% per year).
| Year | Rent cumulative | Buy −1pp reset | Buy flat | Buy +1pp | Buy +2pp | Buy +3pp |
|---|---|---|---|---|---|---|
| 1 | £14,400 | £15,500 | £15,500 | £15,500 | £15,500 | £15,500 |
| 3 | £44,500 | £37,800 | £37,800 | £37,800 | £37,800 | £37,800 |
| 5 | £76,500 | £58,900 | £58,900 | £58,900 | £58,900 | £58,900 |
| 7 | £110,300 | £74,100 | £78,700 | £83,400 | £88,000 | £92,700 |
| 10 | £165,100 | £94,600 | £105,700 | £117,100 | £128,500 | £140,100 |
| 12 | £204,400 | £106,600 | £121,800 | £137,300 | £153,000 | £169,000 |
| 15 | £267,800 | £122,000 | £142,500 | £163,700 | £185,300 | £207,500 |
Three things stand out.
Years 1-5 are identical across every scenario. While the fix is in place the interest curve and the monthly payment are fixed. The only buy-side variable in those years is the upfront sunk cost, which lands in year one and stays the same. This is the structural argument for choosing a longer fix at the outset: it converts an unknowable variable (remortgage rate) into known cash flow, at the cost of giving up the chance of a lower rate in years 2-5.
The buyer is ahead by year 3 in every scenario. Buy-cumulative crosses rent-cumulative between year 1 and year 2 on these numbers; once a £6,000 sale-side cost is added back in at the buyer's eventual exit, breakeven slides to early year 3. The reset rate does not affect this because the reset happens in year 6, after breakeven has already cleared.
Year-15 cumulative cost spread is £85,500. From £122,000 in the −1pp scenario to £207,500 in the +3pp scenario, the cash cost of buying across 15 years swings by an amount roughly equivalent to a year's gross income for a median UK household. The renter's year-15 figure (£267,800) sits above all of them. The buyer still wins on cash-cost terms — but the size of the win is rate-trajectory-dependent.
Why the breakeven horizon barely moves
The intuitive expectation is that a +3pp rate shock pushes breakeven much further out. The model does not behave that way for a specific reason: rent compounds at 3% a year on the same baseline as the buyer's mortgage interest grinds down. By the time the rate shock arrives at year 6, the renter is already paying around £1,380 a month, and by year 15 around £1,755. The renter's escalating outflow eats most of the rate-reset headroom on the buy side.
Two things would change this picture:
- Rent inflation lower than 3% per year. If long-run rent growth runs at 1.5%, the breakeven horizon stretches materially under any rate shock. The Office for National Statistics Private rent and house prices release publishes the official monthly series; recent prints have run materially above 3% in some regions and below in others.
- A larger initial loan, or a shorter fix period. A 10-year fix at 4.32% (had the buyer chosen one) extends the protected window to month 121, by which time most plausible rate trajectories have averaged out. A 2-year fix exposes the buyer to a reset only 24 months into the schedule, before any meaningful breakeven has cleared.
The breakeven horizon is therefore most sensitive to the length of the initial fix and to the regional rent baseline, not to the eventual reset rate. The picture for a Manchester buyer (try a Manchester postcode on the postcode tool) differs from a London buyer mainly because the Manchester rent baseline is lower and the rent-to-price ratio in the region is different, not because the rate-shock arithmetic is different.
Where the rate shock actually shows up: the lifetime interest bill
The cumulative-cash table above runs to year 15. The lifetime totals — what a buyer who stays in the property and the mortgage for the full 25 years actually pays — tell a more dramatic story.
| Reset scenario | Lifetime interest paid | Lifetime total paid (capital + interest) |
|---|---|---|
| −1pp (3.32%) | £142,300 | £412,300 |
| Flat (4.32%) | £172,000 | £442,000 |
| +1pp (5.32%) | £203,100 | £473,100 |
| +2pp (6.32%) | £235,600 | £505,600 |
| +3pp (7.32%) | £269,400 | £539,400 |
The interest-bill range is £127,100 between best and worst case — three to four times the typical UK buyer's annual salary. This is where the rate shock concentrates. It does not break the buy-vs-rent verdict (rent paid over 25 years on the same 3% escalator runs to roughly £521,000), but it materially reshapes how much wealth the buyer can transfer into other things — pension, savings, additional property — across the life of the mortgage.
For a deeper look at the equity side of the equation — how much of each monthly payment actually builds ownership — see Equity built vs rent paid, which shows that at 4.32% on a 25-year term, the year-one equity share is about 35% across every loan size.
Practical takeaways
The model says three things that hold across the full ±3pp reset range:
- The first 5 years are insulated. A 5-year fix at the BoE quoted rate today removes rate-shock risk from the period when breakeven actually happens. The buy-vs-rent answer at year 3 is independent of the reset rate.
- Year-15 cash-cost wins are smaller under high-rate resets but still meaningful. Even at +3pp the buyer's 15-year cash cost is £60,000 below the renter's.
- Lifetime interest is the line item that swings. A £127,000 interest-bill range across the five scenarios is the dominant rate-trajectory risk for a buyer who holds for the full term.
What the model cannot tell you is the right answer for your specific situation. It cannot tell you what rates will be in 2031, whether you will still be in the property in 2031, whether your income will rise faster or slower than the assumed 3% rent growth, or whether your area's specific rent-to-price ratio will follow national patterns. For a worked starting point on the same scenario, see The true cost of buying a £300,000 home in the UK in 2026; the homecost.uk postcode tool then computes the all-in monthly cost for any property on a given street, using the same BoE quoted rate, council tax for the local billing authority, and EPC running cost.
Based on the BoE 75% LTV 5-year fixed quoted rate series and amortisation arithmetic on a £270,000 loan at 25-year repayment. Source data fetched on 19 May 2026.
This is general information, not financial advice. Speak to a qualified adviser before acting on any mortgage decision.