Fixed vs Variable Mortgage Calculator UK

The choice between a fixed and variable mortgage comes down to one question: which costs less in total given what you think rates will do? This calculator takes the guesswork out of the comparison. Enter your loan amount, the fixed rate on offer, and the current variable rate — and see the monthly difference, total interest over any term, and a plain-English verdict on which product is cheaper right now and under what conditions that changes.

Fixed vs variable in context — mid-2025 UK market rates

The table below shows representative rates across the main product types available in mid-2025, from the cheapest competitive deals to the Standard Variable Rate trap. Understanding where each product sits helps frame any individual rate comparison.

Representative mid-2025 rates. Actual rates vary by lender, LTV, credit profile, and product specifics. The SVR row illustrates the cost of not remortgaging when a fixed deal expires.

The most important observation in this table: in mid-2025, competitive fixed rates (4.0–4.7%) are cheaper than most available tracker rates (5.0–5.25%) at the current base rate level. This is relatively unusual — historically trackers started below fixed rates, with the trade-off being rate movement risk. The current position means choosing a tracker over a fix requires a clear view that the base rate will fall meaningfully during the deal period, to make the tracker cheaper in total despite its higher starting rate.

How to use this comparison properly

A meaningful fixed vs variable comparison needs four inputs: loan amount, term, both rates, and the comparison period. Here is what each drives.

The comparison period matters as much as the rates

A two-year comparison on a £250,000 mortgage with a fixed rate of 4.3% and a tracker at 5.0% produces a clear fixed rate winner — the fixed saves approximately £84/month, or £2,016 over two years, even before the arrangement fee is deducted. Over a five-year comparison the saving grows to approximately £5,040 before fee offset. The variable rate would only win if the base rate fell by at least 0.7% during the period and stayed there — reducing the tracker rate below 4.3% for long enough to overcome the head start.

Always include the arrangement fee in the comparison

Fixed rate mortgages often carry arrangement fees of £500–£999, while many tracker products are fee-free. A fixed deal at 4.3% with a £999 fee versus a tracker at 5.0% with no fee: the fixed rate is still cheaper overall because the monthly saving of £84/month recoups the £999 fee in approximately 12 months. But on a higher-rate fixed deal with a large fee and a small monthly saving, the fee payback period can extend beyond the deal length — at which point the tracker might win on total cost even at a higher rate.

The variable rate in the calculator is today's rate, not tomorrow's

The calculator uses a static variable rate, which gives you the cost comparison at today's position. Use the scenario modeller above the table to model what happens if the variable rate rises or falls. If the variable rate drops by 0.5% halfway through a two-year period, the total variable cost changes significantly. Building this sensitivity into your thinking prevents over-reliance on a single-point comparison.

Frequently asked questions

• What is the difference between a fixed and variable mortgage in the UK?
  A fixed rate mortgage locks your interest rate for a set period — typically two or five years — giving identical monthly payments regardless of Bank of England base rate changes. A variable rate mortgage (tracker or discount) has a rate that moves with the base rate or lender's own rate. Fixed = certainty; variable = flexibility and potential to benefit from rate cuts, with the risk of rate rises.
• Is a fixed or variable mortgage cheaper right now?
  In mid-2025, competitive fixed rates (4.0–4.7%) are broadly cheaper than tracker rates (5.0–5.25%) at the current base rate level. This is because the Bank of England base rate remains elevated. Fixed rates only become worse than trackers if the base rate falls significantly — bringing tracker rates below competitive fixed deals — and stays there for long enough to offset any lower fixed rate savings already banked. Standard Variable Rates at 7–8%+ are significantly more expensive than either.
• Should I include the arrangement fee when comparing?
  Yes — always. A fixed deal with a £999 fee at 4.3% versus a fee-free tracker at 5.0% looks like a £999 disadvantage to the fixed deal until you factor in the monthly saving. At £84/month saving, the fee is recovered in approximately 12 months. If your deal is two years or longer, the fixed rate wins clearly even after paying the fee. The fee payback period shown in this calculator tells you exactly how many months it takes to recover the fee through lower monthly payments.
• What happens at the end of a fixed rate mortgage?
  The mortgage automatically reverts to the lender's Standard Variable Rate — typically 7–8%+ in mid-2025. On a £300,000 mortgage this can mean paying £500–£600/month more than a competitive remortgage deal. Start the remortgaging process at least three to six months before your deal expires. Many lenders allow you to lock in a new rate up to six months in advance with no obligation until the current deal ends.
• Can I switch from variable to fixed at any time?
  Most tracker mortgages allow you to switch to a fixed rate at any time without early repayment charges — this is a key advantage of tracker products. Check your mortgage terms for any ERC clause. If you are currently on a fixed rate and want to switch to variable before the deal ends, early repayment charges of 1–5% typically apply. Use the calculator above to check whether the monthly saving from switching justifies any ERC cost.

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