A tracker mortgage moves with the Bank of England base rate; a fixed deal doesn't move at all until it ends. Rather than betting on a single rate forecast, this simulator shows what you'd pay under a falling, flat, and rising rate scenario, so you can see how much the outcome actually depends on which one happens.
How this simulation works
The fixed side is straightforward: your rate is locked for the deal length you specify, so total interest paid over that period is calculated directly from the fixed rate and a standard repayment amortisation. The tracker side recalculates your rate each year as the base rate moves under three scenarios: falling by 0.5 percentage points a year, staying flat, and rising by 0.5 percentage points a year, each compounding over your chosen deal length, with the tracker rate always equal to the base rate plus your specified margin.
Nobody, including professional forecasters, reliably predicts the exact path of the base rate over a two- to five-year period. See our UK Mortgage Rate History reference for how dramatically the base rate has moved, in both directions, over shorter periods than most fixed deals last. Use the three scenarios here to understand your exposure, not to bet on a specific outcome.
What actually determines the right choice
- How much the tracker margin already prices in expected cuts. Tracker margins are set by the lender based partly on their own rate expectations; a very tight margin can already reflect an assumption that rates will fall.
- Your tolerance for payment uncertainty. A tracker means your monthly payment can change at short notice; a fixed deal gives certainty for budgeting even if it turns out to cost more in hindsight.
- How exposed you are to a worst-case scenario. If a rate rise scenario would genuinely strain your finances, that risk itself may be worth paying a premium (a higher fixed rate) to remove, regardless of which scenario is statistically more likely.
If the fixed rate beats the tracker even in the flat scenario (rates staying exactly where they are), the fixed deal is being priced with a rate-rise expectation baked in; if the tracker wins even in the flat scenario, some of that margin advantage is structural, not dependent on rates actually falling. Checking which is true for your specific numbers tells you a lot about what you're really betting on.
Frequently asked questions
Why does the tracker calculation use 0.5 percentage point annual moves?
This is an illustrative, round-number scenario chosen to show a meaningfully different path in each direction, not a prediction. You can compare it against the actual historical pace of base rate change in our Mortgage Rate History reference, which has moved both faster and slower than this at different points.
Does this account for early repayment charges if I switch mid-deal?
No, this compares the two products as if held for the full deal length shown. Early repayment charges on a fixed deal, and any exit fees on a tracker, would need to be added separately if you're considering switching before the deal naturally ends.
Should I always pick whichever option wins in this simulator?
Not necessarily. The numeric result under any single scenario is only one input; your own tolerance for payment uncertainty and how exposed your finances would be under the worst-case rising-rate scenario both matter alongside the pure cost comparison.
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✓ Editorially reviewed — all Poqet guides are checked for factual accuracy before publication and updated when UK rates or legislation change. Editorial Policy