Hundreds of thousands of UK buy-to-let fixed-rate deals end in 2026/27. The borrower who fixed at 3.5% in 2021 may face a revert rate of 7-8% — a payment shock that can wipe out cash flow and fail the lender's ICR re-test, preventing refinance. This calculator sweeps +0, +1, +2 and +3 percentage point shocks on the new rate, recomputes the monthly payment, and re-runs the ICR test at each scenario to flag which combinations still pass.
Interest-Rate Shock & Refinance Cliff
Most landlords are one rate cliff away from a stress test failure. This simulator sweeps +0/+1/+2/+3pp shocks on the post-cliff rate — and re-runs ICR at each.
My scenarios (0/10)
Save snapshots of your inputs to switch between scenarios (e.g. “65% LTV, higher-rate” vs “75% LTV, basic-rate”). Stored in your browser only — no login needed.
Refinance-cliff scenarios
| Shock | New rate | New monthly | Payment jump | ICR achieved | Refi pass? |
|---|---|---|---|---|---|
| +0pp | 3.50% | £583 | +-£417 | 1.53× | Pass |
| +1pp | 4.50% | £750 | +-£250 | 1.53× | Pass |
| +2pp | 5.50% | £917 | +-£83 | 1.53× | Pass |
| +3pp | 6.50% | £1,083 | +£83 | 1.53× | Pass |
Payment jump under shock
ICR achieved by shock
Red bars = refinance fails at that shock level. Target line is the lender's required ICR.
Months to cliff
6 mo
Current payment
£1,000
Worst-case +3pp
£1,083
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Related guides
Plain-English explainers for the rules behind this calculator.
Frequently asked questions
Answers to the questions UK property investors most often have about this tool and the underlying rules.
- How much will my mortgage payment go up?
- For a £200,000 interest-only loan, every 1 percentage point of rate increase adds £167/month. So a move from 3.5% to 6.5% means +£500/month, or +£6,000/year per £200k of loan. For repayment mortgages the effect is smaller in pound terms (the principal repayment absorbs some of the rate impact) but larger as a percentage of total payment.
- What if I fail the ICR test on refinance?
- Two options: (1) take a product transfer with the same lender — many don't re-stress-test on PTs; (2) reduce the loan amount by injecting capital. Failing both, you fall onto SVR (typically 7.5-9.5%) which is brutal. Pre-emptively raising rents in the 12 months before the cliff is the most useful lever.
- Should I refinance early?
- Most UK BTL fixes have early-repayment charges (typically 1-3% of the loan balance) that fall as the fix ages. If rates are projected to rise further, the ERC can be worth paying for a longer fix; if rates are projected to fall, hold. This calculator helps you compare payment scenarios but not the ERC-vs-future-rate decision directly.